I am sure it is not the Clutch (brand new)
The problem is that, in some of the grears, there are sone little "prongs" that fit on the sloted role of the gear rigt aside of it.
When this prongs worn out, if fall out just like when the transmission is on neutrals.
What I have to do is skip the fourth and jump from the thrid to the fifth.
I am surprised that any one of you have had this problem.
We may have a language problem here, so stay with me.
It's not really slipping then. It's actually jumping out of gear, into a false neutral.
If so you are right, its is the side meshing dogs that are worn...OR its more likely a bent shift fork. The longer you run it with a bent fork the more likely you'll wear the dogs more.
Finally, just to be clear, you can't really "skip" 4th gear, going from 3rd to 5th. You have to shift 3 to 4, then 4 to 5. You may not be letting out the clutch in 4th gear, but you can't "skip" it.
You'll have to inspect it by disassembling. Even if the primary problem is the shift fork, you'll likely want to replace the gear as well. And vice versa, I probably wouldn't replace the gear without replacing its respective shift fork.
It is very rare for 4th gear to be damaged and jump out of gear. Anything can happen. It's usually 2nd gear.
