are all your motor mounts good and tight? Yes
do you have to muscle the exhaust into place to bolt it on? No
is the exhaust secured well in all the original mounting locations? Yes
are you using the oem exhaust with no mods - no pieces cut off? Yes
are you over-tightening the acorn nuts? This might be the cause, but would be by the previous owner. I got it with two repaired and then one snapped off before i got 50 miles on the bike.
do you have all the proper parts to mount the exhaust to the head? Yes
any crash damage to the bike? No. In fact, it is in great shape for a 87 model, besides the head.