A new oil leak, different than my others

I'm used to seeing a few black spots on the floor after a ride. Two or three small ones. And the minor leaks around the shift or countershaft seal have been dealt with in years past.

Today a new leak occurred and though a few searches have been done I wanted to post just to see if there was an obvious "ah ha" reason.

YZ250 (Bought the 09 used with the promise of "it has a new top end" but we know how that usually goes) which I have been running 40:1 the last month. The only change from the past 30 days was I borrowed half a gallon of 50:1 and ran the bike very hard at the end of the day; two runs down a top gear pinned sand wash. Thirty minutes later there is golden motor oil (not burnt premix) in my truck bed and a few hours later there is motor oil all over the bike stand. At first thought a rock put a hole in the case or my drain plug somehow came loose. Nope and nope. Tight and drip free everywhere except the leak from the black hose coming out from the left side of the cylinder.

I'll sleep on it and dig into the situation tomorrow but my main question is why is motor oil dripping out after running WOT with a little bit of 50:1.....or is that independent of the main issue?

May be time for a new top end or a new #6 seal but it never hurts to get more info before tackling a job. Thanks in advance.

I've seen my previous bikes puke gear oil after long W.O.T. runs. It foams up the oil or something after high speed W.O.T. runs, which then leaks out the overflow. What color is your gear oil? My 250 hasn't done it but my previous bikes have after long straightaways at high rpms.

Thanks for the input. The motor oil color looks fresh as if straight out of the bottle (since I recently changed it). Upon further inspection/good night's sleep - and after taking glide plate off and pressure washing everything - it is mainly my shift shaft seal. The leak is there even leaned over to the left in my garage. Thankfully local dealer had seal in stock and it's a quick fix.

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