Any discussion involving an oil tends to be a slippery one!
Don’t sweat the small stuff and this is small stuff. Dry or wet clutch, I check level and condition each weekend, change it each season when the cases get cracked open. A season for me is about 4 road races though, so say 8hrs of running, some run a lot more in a year. The car oil analogy doesn’t apply as you don’t (or at least shouldn’t) have combustion byproducts in your gear oil!! The gear surface area is pretty large in these transmissions compared to the torque that’s being transmitted through them.
I think you could argue either way as to whether MotoX or karting is harder on the tranny. Sure you are WFO in a kart a lot more, but think of the aggressive loading\unloading that happens on the motos. Then there’s the dust…
Sure, every little adds up, but you have to draw the line somewhere and without any real evidence I think this is where I would draw the line. Check it once in a while, you’ll be fine, and yes I’m talking about oil bath clutches too.
If you really wanna nerd out, get a UOA done on your used transmission oil, that will tell you EXACTLY whats going on: Viscosity, additives remaining, contamination (gear or bearing material) etc etc.
ATF can be used (ever pull apart an auto transmission?….series of wet clutches in there) but I’d only do it with fresh plates. Otherwise, just run a good “racing” motorcycle-type gearbox oil, check it and let’r buck. Personally though, I think in this case its a good idea of have the extra anti-shear properties of the racing gearbox oil.