So I'm in the process of doing a Mark 7 upgrade to the whole thing and I'm at the part where you replace the spindle on the sanding disc.
On problem...getting off adhesive backed sandpaper that's been on there for over 20 years.
Oh, the sandpaper part came off easy enough, but it left a layer of paper and the plastic film with the caked on adhesive behind it.
Here is what I want to share if anyone else comes upon the same issue.
Get yourself some Rapid Remover (http://amzn.com/B006RUJ2D8), I happend to have this because I use it to remove stickers from vehicle bumpers and fatory emblems that I don't want.
Well, this stuff also works great on this residual sand paper adhesive!
Get it really soaked and let it dwell for 15 minutes or more, just be sure that it doesn't dry up while you're waiting.
Then get after it with one of those plastic SaferScrapers (http://amzn.com/B005DVHV0S)with the plastic blades and the stuff comes completely off with just a little effort.
Thing looks practically brand new at this point and ready to have the velcro sanding package applied to it...cause I don't want to do this again
Hope that helps someone else who might be facing the same issue.