Steve S - I agree with Steve B, Mr. Plow - but it could also be the other way around. The steel button or fingers could have damaged/broke the fiber button.
You should be able to look at the PTO clutch when the tractor is running. If you see the PTO assembly rotating (everything inside the basket pulley) then the PTO is basically operating, and as long as you have a belt on the pulley going over your mule drive to the deck, and the belt on the deck pulleys, then the deck should be spinning.
If the PTO assembly isn't rotating when the engine is running, and there is no fiber button pushing on the steel button, then you definitely have something wrong with the PTO clutch assembly, and you almost certainly need a rebuild.
There's no telling what's wrong until you get a closer look while it's still mounted to the tractor BUT with the engine NOT RUNNING. I'd remove the grill so you'll be able to get a good look. There should be 3 ear type items that slide into the steel center button. If they have come out then you're spring may have broken, or the steel button itself may have failed.
Most likely you'll still have to remove and disassemble the PTO clutch before you can really tell what's gone wrong. The Service Manual will help you a lot but you'll have to inspect the parts to decide what may be bad. I'd probably just get a complete PTO Clutch rebuild kit, and also a new PTO bearing and locking collar while you have it off. Just as well do the entire clutch and bearing and it should be good for another 20, no 30-40 maybe even 50 years.