Seeing as I am the seller of this amp I might as well chime in here...
First off, I bought it off this forum from forgivenman. He told me it was running perfectly, gave me "the tubes have a lot of life" line, etc... so I bought it and found out the 2 6L6's were old and mismatched (427, 430), the capacitors were fried, the bias needed to be reset for mesa tubes (was messed with by probably another previous owner) and there was broken glass in the cab from some kind of EH tube.....real nice. I bought brand new Mesa El34 and 6L6 power tubes and had it fixed up. It cost me about $200 for everything.
I recorded with it for about an hour and realized my Mark IV was more to my liking so I took it with me as a possible trade for a 3 channel DR. We fired it up, sounded great, no noise, worked perfectly, good gain on rhythm 2 and lead with a slight gain increase on the lead channel. We both agreed that the DR had a lot more gain which was to be expected. He didn't take it for a trade, but I still bought the DR.
Listed it on ebay about a week later, original poster bought it. I packed the hell out of it and sent it off. He emails me saying he can't get the pedals to work and there was minimal lead gain. Eventually got the pedals working, but tells me there is still not enough lead gain and it doesn't sound just like some 80's recording he has. Unless you're in the 80's at the same time, same studio using the same gear it never will!
Emails me again threatening me with negative feedback if I don't give him his money back for sending a "Nonfunctional" amp. Nonfunctional means not working, broken, etc, it doesn't mean not enough gain for your liking. I have told him to take it to a tech and have it checked out. My guess is that there might be a problem with the lead push pull or possibly a previous owner had something done with the lead channel. The tech didn't see it and I've never played a Mark III before so I had no idea how much gain to expect. According to another post, a diode looks overheated, etc.. If something happened in the short time it was played or if the tech wasn't up to par, I wouldn't know and I definitely couldn't hear a change. It was played for literally 2 hours after being worked on. I told him to have it checked out and whatever repairs (if any) would be very little. Try new preamp tubes, etc. I even mentioned having a gain mod added for the lead channel if that's possible.
Bottom line is he got a very nice Mark III with a rhythm 2 volume mod, brand new power tubes, bias correction and new capacitors. He's complaining about how he spent a few dollars more, etc... I never called forgivenman to ***** about the condition of the amp even though I easily could have gotten my money back. I put a lot of money into the amp and took a loss selling it. I can't even remember how many times I've bought an amp, dumped a bunch of money into it, didn't like it and sold it. That's what we do, buy and sell, live and learn. It will cost less to have it checked out/modded than to ship it back to me anyway. If you want more gain, buy a freaking rectifier!!!