As the quartz crisis was raging, various companies made direct drop in replacement quartz movts for mechanical watches. These movts are getting harder to find nowadays, because the demand has dropped right off, but there were a LOT of old watches converted back in the day. I especially used to see a lot of ladies watches converted, and the reason is simple: Pay far more for a proper overhaul of the mechanism, or get a quartz movt that keeps near perfect time and costs a fraction. The trouble is, when there were no movts available that would fit the cases, (With or without plastic spacer rings) there were various putties and compounds available. Some would 'cure' like epoxy and become a hard, plastic-like substance, and others would remain fairly pliable. The soft ones don't work as well, but do less damage to the case.