I just finished another 100 hour inspection on our RV12 (SLSA). We are putting about 70 hours a month on it.
About a month ago I ordered a new gear set and dog gear for the gearbox. If you remember, I couldn't idle much below 2500 rpm cold, due to vibration and gearbox chatter. I rebuilt the carbs, balanced them many times etc. But it didn't cure the problem. Aircraft only had about 120 real hours on it when we got it.
So, yesterday I cracked it open. I have to say that Sensenich is a bit barbaric in their prop/hub/bulkhead assembly on the -12. It's at least a two person job.
But, once I got it opened, I did see a lot of where on the dogs. Way too much wear for such a low time engine (about 400 hours now).
I wasn't happy to realize that CPS hadn't sent me the dog hub yet, just the gear set half. Since it's in a flight school, I had to put in what I had, and go with that for now.
But what a difference!! Now it runs smooth all the way down to 1600 RPM, with no chatter above 1800 rpm.
I'll open it up again when I get the other side of the dog gear and put that in.
The previous owner was very meticulous on how he operated it. He took Rotax and LSRI classes, and kept an incredibly well detailed report on each annual. He used AeroShell Sport 4 oil, and almost always used 91 octane fuel.
I have switched over to Mobile 1 4T oil. I have no other smoking gun than oil to blame for the early wear. I understand that Rotax has an obligation to promote the AeroShell oil, but I just don't think it's as good for the gearbox. I run about 95% mogas in the -12.
Another reference source: I just did an annual on a Tecnam SLSA, which has also been running the Aeroshell. It ran rough as well, with excess chatter.