#3 (or is it #2?) vote for disc installed backwards. The springs stick out too far to be installed toward the flywheel. Probably didn't make noise because the bolt heads had been ground off enough to clear the springs. Time for a new clutch AND flywheel bolts. BTW, the bolts are not standard as far as head height - they have heads that are shorter than hardware store bolts.
There was plenty of head left for socket to grab, so removal wasn't difficult. But yeah, new bolts for sure.
Doubt if the clutch in my 3100 is 11" but I'll be happy to use the 11" when time comes to switch everything. Came with starter as well, so tooth/ring gear definitely match.
Before disassembly I stuck my finger in the pilot bushing and it came right out, no tools, no nothing. Kinda odd.
