I'd say use it until you break it, or until the tank starts leaking.
My Grandfather's old Sears compressor still works perfectly fine, but there is a leak in the tank and I've read one too many horror stories to be comfortable using it regularly, so I've left it in his old shop on the homestead and use it to air up tires/blow stuff off but I never let too much pressure build up in the tank.
If I could find a tank that fits and looks right on it, I'd switch it over and use that instead of my current C-H 20 gallon, I just love the sound of that old Sears compressor and it brings back so many memories.
