Leica M3 curtain light leak query

I have had an M3 serviced early this year but have only just finished the film and developed it. About 9 out of 36 exposures suffered a similar light streak although one had it in the middle. The rest were okay. Most photos were taken at 250th & 125th. It looks like the closing curtain is not going into the opening curtain channel correctly. Is this a simple fix like cleaning the channel and applying the barest of lubricant to the channel? Or tweaking the tension a bit on the closing curtain? Otherwise it's a long drive to the service guy on the other side of town.

My wild guess is an obstruction in one channel that the edge of the shutter travels in. It could be a particle or stray lubricant. Lubricating the channel sounds risky.

Never wait this long to check any camera. "Other side of the town"... I have to drive from my town across another city to get it serviced in the next to it city.
Your service guy did same job, just like guy I gave to did with my M4-2. Light leak became worst after his service. I returned camera quickly after taking few rolls of film. With negatives showing the problem. And... never heard from him since March....
Leica is not so easy to own camera these days if you are non in USA....

There's nothing so humbling as having to tell the service guy you heard something snap when you tightened the roller.

Then there was the Spotmatic F that I thought I'd just fix the capping by adjusting the spring. Snapped the pretty red painted setscrew with the first twist.

I'd rather leave it to the service guy, that's what I'm leading up to.

There'a no lube in the curtain channel. The curtain's fabric and won't do it any good. But if you want to
contribute to your techs retirement fund........

All fixed, fortune favours the brave. Closing shutter curtain needed half a screw of more tension to make its channel end fully mate with the opening shutter end bar. Where would we be without YouTube repair guidance!