GruBee Stage III Gear box lubrication

I run a Hua Sheng F142 49cc 4-stroke engine with the GruBee Stage III Gear box and a Sick Bike Parts shift kit. After taking my bike out of storage for the winter, it now appears that my gear box needs lubrication.

A few moments after I start the engine, the gear box gives me a horrible shriek-ing sound and my wheel starts to turn at a low idle speed. Gunning the throttle does not appear to help at all. If I engage the drive, the noise stops, and the the centrifugal clutch takes over. But again, my wheel is still turning at a low idle speed. The sound reminds me of something spinning fast that desperately needs lubrication. The problem is especially acute when the engine is cold. The sound eventually disappears when it has warmed up a lot.

I am afraid to start dumping lubricant into the gearbox because I don't want to contaminate the centrifugal clutch. When I looked into the correct lubrication regiment for the gearbox, bicycle-engines.com says, "We recommend using a 50/50 mixture of Lucas Gear Oil (85w-140) and Stop Leak to lubricate the internal gears and help prolong the life of your gear box."

But according to the GruBee website, "Add approx. 50 to 80cc of 10wt. HT machine oil to cover bottom portion of gear 19. Gear Rotation will splash oil upward."

Can anyone explain to me why one is better than the other? Do I need to open the case and apply lube to a specific part? Am I worrying over nothing and should I fill the gearbox as recommended? I'd like to avoid visiting the mechanic if I can.

I've seen a related bushing discussion elsewhere in this forum. Is this clutch bell bushing the same one that people have said was an Oilite Bushing but without the oil? Is there any way to tell if it is Oilite or if it is properly impregnated with oil?

I purchased the kit last summer from bicycle-engines.com, so I'm betting it is the newer version. I'll post pics once I open up the case. Hopefully then I can answer for sure whether or not it uses individual coil compression springs.

Here are pictures of inside my gearbox, and I think I found my problem.

The final gear in the gearbox is supposed to spin freely while the 6-tooth engager is not engaged. When the gearbox is engaged, the 6-teeth mesh and power goes to the primary chain and so forth to power the bike.

However, if the final gear is not lubricated, it can grab at the shaft without involving the 6-teeth at all. In the third picture you can see a silvery-brushed band on the shaft. When I put my finger on it, the metal was completely dry. Even when I put the final gear back on and spun it with my finger, it made a bit of a honking sound.

So after my little experiment, I spot-greased the final gear and reassembled the gearbox. Since then, I've put on about another hundred miles and it hasn't made that horrible sound again.