I bought an eco 97 wall mount unit a few weeks ago on ebay and performed a basic restoration on it. After it arrived I opened it up and surprise, it turns out the inside was a safe haven for a few million mice over the years so besides smelling like a giant urine filed diaper, their years of living in there literally eroded the metal on the harp and the front and back inside covers. After a week of taking everything apart (which included breaking three bolts, then drilling and tapping them), extensive cleaning and sandblasting finally got her back to painting condition. I used urethane primer and paint and I also replaced the old worn parts with new replacements. After I installed a new diaphragm and strainer gasket it sprung back to life (don't know how accurate it is but it's really used as a display for me to look at in the shop/garage/man cave). Here are some pics, it's not up to the standard of a Jack Sim restoration but it looks pretty nice on the wall.

Wally