Don't worry about the heat if you are using an oxy/acet rig. get in with the heat and get out. I wouldn't worry about a purge gas either, doesn't hurt but I wouldn't worry about it. Use a wet rag to cool off. And I would at least quote a new compressor, you have done your honest attempt but there might be more problems down the road. Also no need to a vibration absorber, they didn't come on it originally, if it is shaking that bad the compressor needs to be changed.
Another point if this is MP39, this dates this unit and the customer needs to know that in the long run this is on its way out. I am sure the whole thing has seen better days.

And on the topis of solder, my company uses 5%. It is cheaper, but if you clean your joints and use white flux when needed it works fine. But we do carry 50/50 for those dis-similar metals.