That saw is 40 years old, they switched to red from blue around 1970. Do you live near the coast? A combination of moisture, oxygen, and possibly salt has gradually eaten away the aluminum. It is a common problem.
You won't find much for new parts.A coating of JB Weld may help, be sure the metal is dry and super clean.

the saw is definatly not 40 years old,,, I bought it new somewhere between 91 and 93, it was a special edition called "old blue" ,,, I will try to get the ###s tonight

The best I can tell the model number looks like 10712 I cant read the S# at all.
maby I can get a magnifier and come up with more later.
I live about 40 miles from the nearest coast, we don't have a salt problem that far away. The saw has never been used close enough to the coast to cause the problem either. I am guessing your right about the moisture in the air,,,,,,, BUT why ONLY on the bottom of the saw??? you can see all of the paint intact,its just bubbled up,,,,, what ever it is has crept under the paint and is eating away at the metal. The top looks great with no sighn at all of the decay even starting.
It has a chain guard on it and the saw has been stood on the tip with the saw head stuck up in the air for at least the last 10 years.
Ill check back later "maby with S#,, to see if any one can find a case..... and if any one knows a better compound than the JB weld for a temporary patch job.
Thnks for your help

Is it possible that while it rested on its blade tip that the bottom of the saw was leaning against a piece of treated wood like a CCA (Wolmanized) post? Maybe electrolysis between the copper and aluminum? Or (reaching waaaay out there)maybe the saw was completing a ground circuit for a low level current, maybe humid weather and a battery charger, fence charger, freezer, etc?

Yea ,, That all sounds logical but the saw was leaning against a regular 2x4 stud by the plastic like hand guard. It is dry inside the building except for the moisture in the air. No electric in the building except batterys in mower & motorcycle unless I drag a cord from the house to charge a battery or blow up tires. It also has a plastic chain guard so I think we can ruel out that part. The only thing I can come up with is their was a spoonfull of dirt packed in at the case below the chain probably where I cut a few small trees at ground level the last time it was used,,,, that dirt and moisture in the air could have caused it to oxidize or what ever aluminum does as rust to metal..... But I am past that part,,I need to focus on how to patch or fix it. Although it will help others to be sure their equipment is clean and oiled regularly even if in storage. If I had pulled it out and cleaned the spider webs dust etc and sprayed it all over with a light penetrating oil once a year it would probly not have done it or I would have at least noticed it long before it got this bad,
what I need to know is, what can I patch the [I guess] cast aluminum with that will withstand gasoline untill I find a case or figure something else out.
The case is barely leaking gas right now but it is still a fire awating to happen. you know ,, one spark aimed just right close to one drop of gas = fire.
So if any one knows the best patch material for this aluminum case that is compatable with gas let me know... Or if you can get me a new or used case with the number I gave previously.
Thanks to all

JB Weld makes a gas tank 2 part putty that will fill some good size holes. Then over coat with regular JB Weld. I would use ether or brake clean to prep surface after wire brushing or sand paper. Allow 24hrs for each coat of epoxy to cure.

thanks for the info Andyma,,,, I have seen the two part mix sticks for gas tank repair and thought about them, I dont know if what Ive seen was JBW or not.... I will finaly be able tomorrow to get out and look for something to fix it with,,,
thanks for all of the help
I hope this will help others prevent the problem.

A cast aluminum light kit on one of my ceiling fans
did the same thing. It would break apart in your fingers
like a saltine cracker.