I believe this rebuild kit would allow you to rebuild it your self.

Midland-Ross Rebuild Kit

I am not a '70's guru but IIRC the Midland boosters are plated, not painted. I've seen people take the painted Bendix units that were rusty and skim coat them with JB-Weld and then repaint them. I don't think you have that option. Surely there are used units out there that may be a better choice. Good luck.

"We live in a time when intelligent people are being silenced so that stupid people won't be offended".