If you know the model number you can go to the link and find the owners manual. They are free. Stihl Instruction Manuals

I found a copy - no mention. Guess Ill look through other model manuals. or play it safe and just grease it 1x per year.

While not a Stihl, I use an Echo SRM2100 which is a straight shaft with flex drive, so similar to yours. Echo recommends high temp lithium grease and says to do every 25 hours. Myself I take the shaft out and grease every other year. Been running strong for more than 14 years.

Annual is the norm as advised by gg . Any high temp grease will suffice , I prefer Moly but Lithium is good also . If you were in a commercial usage situation then by Bi-annual may be more appropriate service recommendation period but for normal residental use once a yr will be adequate..

Thanks Guys, Ill stick 1 / yr. BTW, anyone know what the lube stihl sells is? I know if u mix different types of grease, it will turn wattery.