Dick.... buddy.... come on....
If you have had that thing 30 years and it has given satisfactory service, you should be giving it a Viking's funeral. Take it from me, a great deal of those less expensive, medium quality tools just aren't worth fixing.
I used those saws in the 70s when framing houses. I used to go to the pawn shops and buy them for $20 - $25 a piece and run them to death. They were perfect saws for my knotheads, and I sure didn't want them using my Rockwells or Milwaukees.
Do yourself a favor and get a new double insulated,
15 amp saw with metal gears, roller bearings and easy to replace brushes. You will forget about that old Sears pretty damn quick after using one of the newer saws out there. Plan on spending more than we used to in the 70s though, probably in the $125 - $150 for a good saw.
There are plenty of saws out there less than $75 bucks or so, but they usually have sleeved shafts (no bearings) and are made from lousy components.
I know what it is like to have a favorite tool and get attached to it. I recently went on Ebay and found an old Milwaukee saw (exactly like I used in the early 80s) that has been discontinued for about 20 years. I bought it in a fit of sentimentality and I am glad I did. It is great, but I never take it to the job as I know there aren't any more of them, and certainly no parts other than triggers and bearings.
But honestly Dick.... time to buy.
Robert