I was working this today, on my 240 D, because they've never been done. Both 8mm bolt holes were exceptionally clean.
Sprayed with penetrant too.
I ran an SK top quality Allen, on a 12" snap-on ratchet (your point of needing 1/2" drive noted; I have 3/8). Both bolts moved the slightest bit, like let's call it one degree, then wouldn't go any further.
As I hadn't read your comment here on constant pressure (which is why I'm replying here, as it's good guidance), I put my 3/8" impact on it. That's good for what, 200ft-lb max, likely less?
So I stopped. I have an 18" or so 3/8" breaker. Obviously I can extend it with a pipe.
Question is, how much is too much? Is there a good rule of thumb for when I'm going to do damage?
When I did mounts on my '82, the bolts came out easily. I was expecting the same since this car is so clean and low mileage.
Id hate to ruin the bolts. Kent from Washington says that a rough idle or a compressed mount can beat the threads such that they're damaged and don't want to comply. The only complaint on this car is that at slow idle it's rough in drive with AC on. Fast idle and driving it is smooth as glass. But if this theory of Kent's is true, there could be damage on the threads.
I'd expect these to come right out. I'm surprised they won't. How long of a breaker is typically used?
Thanks!