I would not recommend painting it yourself...the bubbling you are experiencing was a problem with later M6's when they switched to zinc top plates...
had something to do with improper cleaning and prep prior to the final surfaces being applied...was a hit or miss deal. Often, if surfaces got scratched, humidity accelerated the issue.
A good working M6 in 8+ condition should fetch around
1200-1400 on Ebay, but painting one of these cameras, always ends up looking like crap...and you may actually hurt the value.
I've seen many and you'll end up having a harder time selling it...you may just want to sell it for a lower price and move on. As soon as I see a bubbling M6 listed on Ebay,
I immediately skip it, as there are many good specimens to choose from. Generally, Leica users are a finicky bunch, and not prone to accepting un-orthodox repairs...unless
you really know how to do high end refinishing work, I wouldn't waste your time.