The deformed leaves are a result of peach leaf curl. The reddish/brown/black globs are some kind of scale. Ants are feeding on the honeydew of the scale. So there may be nothing wrong that a few sprays won't cure. Well maybe a little fertilizer, prune out anything dead, and spray.

To be more specific, spray 3 times with Microcop or something similar, the first time after the leaves fall in early December, again around January/ February, and again right before the buds open.
I think will be amazed at how your little tree is no longer "declining" next year if you spray! It probably has been suffering through the un-sprayed disease all these years.

Carla in Sac

And squish the scale.

Thanks. I'll forward the comments and my copper and neem oil the next time they visit.

I doubt I can convince them to squish the abundance of those red "balls". Really, they are scale? Some are the size of grapes, the majority are large pea sized.

Anyone got any technical links to the type of scale this is?

The UCDavis IPM site doesn't have anything like it that I could find. The closest by picture (in egg form) is European fruit lecanium

I guess I'm lucky to only have encountered smaller soft brown scale.

I have this also on a 5 year old tree with a lot of fruit. No ants seen and when I remove the "scale" it is dry and crumbles easily. It covers my branches but the fruit looks fine and leaves are normal looking.

Really need to know how to treat this, I sprayed "7" on it, I don't know if it will help.