Thank you for the explanation Advantage. Sounds like they have been working with you. I know some of the first units had shifting problems, but I thought they worked through that. Did they replace both upper gear sets? I know my SCX shifts very nicely. But mine is newer than 2010. I hope you have better results with them this time. I am running Royal Purple in mine. And it is too early to really see any wear. I did start to drain some oil from the drive and it was clean. So I am going to add some hours and then check it again. I was running it with a small prop, so not much load on it.
Let us know how it goes..

thinking about switching drives anyone else running the scx 4 surface drive?