Okay, I have been having fun but if I do some long runs or hard turns the rear left wheel comes off. I have tightend it but not too tight. Should I wrench it down or use thred lock?
This is a common problem with the slash. The lock nut doesn't go on far enough to get to the Teflon ring in the nut. One fix is lock tight or a cleaner easier fix is to get a Teflon insert lock nut.
Go with the threadlock gel or the threadlock stick. I've had minimal success at using the watery stuff for larger threads like axles. The blue threadlock gel holds up really well and does a really good job.