CFR, I got it used on Friday, I'm now it's 3rd owner. Apparently the first owner didn't give the guy I bought it off the slipper tool, and that it ran fine. This may be the case, and my brushless has just worked it loose.
I will also give the diffs a look (may as well, seeing as it's used), so thanks for that Legend.
Super__dan, thanks for all that info, I will buy the slipper tool when I can, but I have the spare parts to rebuild it if the pliers do damage, and it means it can try it now. I will probably run it nearly locked. I locked my mini inferno, and prefer the feel of an immediate kick so to speak
I have a spare belt anyway, so if I get excessive wear I can always back off the slipper clutch and fit the new belt.
Thanks for all the help, hopefully you've found the problem!