What Torx are you using that it snaps off or rounds? IVve had ZERO issues with that bolt on my FS85...maybe it's the tools and not the bolt?
The Stihl supplied T handled twisted, a Dewalt bit twisted, another bit, no idea what brand, but my father has them in bulk, it's what they use for roofing at his company (should be good quality) also twisted, some other unbranded or unmarked bit broke. I'll take a photo tomorrow if I still have the Stihl tool (am at work right now and after I get home I'm going out with some old class mates).
1) Maybe don't try removing the grease plug when hot? (the resultant expansion might be making the plug tighter due to expansion of the alloy casting especially against the underside of the plug flange).
2) You could try grinding the end of a socket to remove the internal chamfer/lead-in - this will allow the socket to engage with the full depth of the hex on the head of the grease plug and might avoid rounding it off. Or do the same grinding trick on a box end wrench (ring spanner).
In Europe :-
TengTools list 6 point sockets in size 1/2"AF - item number for 1/4 drive is M140116-C, 3/8 drive is M380116-C, unfortunately the 1/2 drive is a 12 point, but they do list a 6 point Impact socket in 1/2 drive - item number 920116.
Sealey Tools do 6 point sockets in 1/4, 3/8 and 1/2 inch drive but afaik, they don't supply individual sizes, just sets of sockets on a rail.
Hth,
~Tostal.
1) Greasing is done before use, not after, so it's ice cold.
2) Not a bad idea, but too much work.
Sockets are no problem. I can get those from basically every manufacturer even in SAE sizes. What's not available is a 6 point box wrench, only 12-points.
We routinely torque T-20’s to 90 lb\in, without camming out or breaking tips. When we do tear them up, it’s due to idiots way over torquing on installation, or thread galling.
Can't remember the torx size, but it's clearly undersized. If you look at the sample photo you can see they could have used a much larger size. The "idiot" in this case is called heat. I could tighten the plug with my bare hands and I'd still happen.