I don't know about replacing a wire but i have a 300 that i have stagged the bottom side brushes with the big fowler brushes and it helped some. check your throttle linkage i have heard the new ones back off easily and that would cause your ocv's to go up.
Mine is a 2008 and it was way watery at first but what I started doing with it was turn the machine all the way up, get a piece os scrap and stick a 3/16 rod to it until the rod melts. Do it as long as you can stand the heat, let the leads cool then do it some more. Mine didnt settle down till about 1300 hours. Good luck!
Load bank it check ocv set arc control bout 6 it worked for me mines a 2010 with 1900 hrs changed brushes at 1600 went with factory brushes . A friend of mine has rolled rack in his poured water and vinegar everywhere but the problem might be a short from shoulder to the holder in his situation it's a little cold to me
fowler brushes will make a difference they wear out alittle faster on the down side. depending on what machine you were previously used to this one will take alittle to get used to as well and probably will be alittle hot untill it settles sometime around a thousand hrs. 300d's tend to be alittle more on the watery side anyway when compared to other machines.
Ya I agree that its on the cold side. I have to run hotter with lo hy or downhill. I did run about 20 lbs of 3/16 lo hy threw it on Maxine when it had about 60 hrs on it. It never has tried wet stacking on me n I heard if u make it past 100 hrs u should b alright. I guess ill try some Fowler brushes. Somebody told me these machines have 200 brushes in them is that true? N what should I put back in it?