Arse. Tried to renew my gearbox oil today and of course both the filler and drain bolts were stuck fast. After some huffing and puffing tried a little bit of WD40 for 20 minutes. Came back, still no luck. Used a torque bar and the drain bolt was just too soft and ended up being rounded off. So I'm a bit stumped now, any ideas people? I can get the mole grips on it still and there is still some reminents of the bolt left (ie only the corners are rounded). A 13mm socket will just spin freely now though. Filler plug is still ok but was going the same way as the other bolt so I stopped. I can think that a blowtorch might help but seems a bit drastic.

Definitely concentrate on the filler bolt first...and getting hold of replacements

At this stage it's a tricky one... tricks of the trade I've heard are welding on another nut ontop of the plug, and hammering on a smaller socket eg. 12mm to a mashed drain plug

id weld on a bolt or thread on to the rounded bolt
if you can then un thread it

I'll have to give my mate a ring with the welder then. Wish I could afford one

Try hammering on a smaller socket, especially a multi cornered one (not 6 sider), 6 siders are better if they are not too damaged, and should always be used on high torque or suspect bolts to start with.

Also chisel on a corner and hammer, on an undoing side of course.

Summurised procedure:
Heat, hammer, bigger hammer, weld, hammer, bigger hammer, bin

I'd suggest drilling them out, but it'd cause more trouble than it was worth I think. Or maybe a bit of heat on it? Careful....

Hammering on a smaller socket may be the sensible way to go...

I'll try and get an angle on it, it's a tight space to hammer in there! Cheers

Angle GRINDER i hope

THis has become my favourite tool for removing rounded off/stuck bolts which I have replacements for!