We ripped out linoleum in our kitchen and sanded away the black tar and were left with spots where we needed to replace boards we used the wood from within our closets and it was feathered to blend in. It worked seamlessly for us.

Good luck I hope you can keep the floors! Nicole Curtis always stains her unpatchable floors all dark to hide flaws that might be an option too.

Are you sure that can't be sanded off?

I just had a floor refinisher do a spectacular job on old hardwood floors that had some black staining on them in spots. He said they wouldn't be perfect when he was done and he was right, I can still see some faint outlines of the worst of it - but that "old" floor is a heck of a lot nicer than I ever expected it to be. It has the perfect amount of patina to go with an older home.

My floors looked similar to yours when I ripped out the old carpets. The first guy I consulted told me I'd have to remove the black gunk by hand... I worked long and hard and barely removed any, so I had another guy come take a look. He said he could just sand it off with a machine, so that's what I had him do.

Re repairs: my floors are narrow tongue-n-groove oak and I had a large area w/ severe water damage that needed to be replaced. The floor guy with the machine told me to chisel out the bad pieces, staggering the cut lines randomly along the bad boards. Then I went to a hardwood lumber shop and had them cut pieces of oak to exactly fit the pieces I had chiseled out. Since there was no tongue/groove, I just glued the new wood pieces down. My repairs came out *great*!

I had a big prominent area in my dining room--probably pet urine stains--patched in my previous 100 year old house, with wood taken from closets. No one could tell when it was done! Keep getting estimates. It is really amazing how such horrible looking floors can be beautifully renewed.

Use the original. Patch then sand and re-stain and finish all to match. Very cost effective way to go.

The original oak floors in my 1939 house were refinished by sanding down. Once sanded, they looked like new oak.

We patched in oak in wider pieces for the expanded openings in the dining room.

Then, in the new addition, used the same width oak, but new.

It all looks the same. No need to rip out all your good hardwood.

The refinishing here was $2.50 per sf.

I had old wood floors in my last house and I was amazed at the variety of wood floor refinishers as far as quality of workmanship and also reliability, etc. Your floors can be fixed and when finished you will have something much more valuable than what it would cost to replace the whole thing with something even half as similar. That is, IF you can find the right person to work with. It's fussy work and you need to be creative and thoughtful to figure out how to do it, not necessarily a skill set the average woodworker has, but some do, the ones who are in it because they love working with wood. Perhaps you could find someone retired or semi-retired who doesn't mind doing small jobs. I'm lucky, I'm in a relationship with one. I keep telling him that there is some work out there for him if he were to go semi-retired.

I had a big square in the dining room that was plywood and my floor refinisher used NEW boards to replace the plywood. My floors were 80 years old at the time and I cannot tell where he did the repair -- I know the approximate area but I can't really tell. A good floor man should be able to do it.

You might want to post this on the Old House forum and get the perspective of some old house experts. I have a 100 year old + house in Virginia and was able to buy replacement boards from an architectural salvage store in Richmond, VA.

Ditto what others have said. When we moved in and had the carpet pulled up we had horrible floors refinished and patched over a large grate and several boards replaced with new boards and even I can't tell the difference knowing where the problem areas were. You just need to find the right pro.

I've done several wood floors renovations in old homes; the only one we had to replace was where the pet urine stains were just way too excessive. Judging from the pictures those are relatively small areas to patch that can probably be done from flooring taken from your closets. Also if there are stains the boards can sometime just be taken up, flipped over and reinstalled. You need a more experienced floor guy.

BTW that wooded return air grate in the first picture is both expensive and hard to replace so if its in reasonable condition you'll want to keep it and have it refinished as well.

Is there any wood in a bedroom you can steal? You CAN match old flooring and new. It just takes a bit of time.

That black crap often comes off with a steamer and scraper. Or soy gel paint remover. Do some testing. You might not have to do a full sanding.

Buy unstained bundles of oak tongue and groove.

IMPORTANT: If the old flooring has been sanded, it will be thinner than the new stuff. Use a planer and remove from the TOP of the new boards until thickness matches.

here's matching new oak to old oak and older pine ...
http://st.hzcdn.com/simgs/12f2ebf504ae5367_8-0761/home-design.jpg 

My method:

1 - Ignore color names, and run stain tests on the new flooring,
comparing with the old floor by laying the samples on the old stuff, parallel to the boards and
seeing what blends. ***Sand and stain just like you will for the real
floor.***

Doesn't have to match, just blend shades and have the same undertones. For oak, it's shades of golden and reddish brown.

2 - Pick three colors that are close to a match with the existing
boards. Match the darkest, medium and lightest shades. For this floor,
it's Minwax Golden Mahogany, Light Cherry, and Birch.

3 - Sand and stain the individual boards before installation. About
20% darkest, 20% lightest, the rest the middle shade. This mimics the
natural variability on an old floor, where different boards have reacted
differently to light.

I shoved several pieces together and sanded and stained them as a group, then took them apart for install.