I had the same issue. Tried the vise - didn't work, tried heat - didn't work, tried wd-40, didn't work. Even tried the chisel - just ended up cutting the collar off. Long story short, I finally got the insert out by using a pair of channel locks + a mallet. This may sound stupid, but a good pair of channel locks can take the abuse, and it only took 3 or 4 hits. Clamp the channel locks on to the collar and hit the handle so that the channel locks tighten. This was the only thing that would have worked - I even tried taking it to a machine shop and they couldn't even get them out. Also, the problem with a pipe wrench is that it slips, and even if you get a good grip you just end up twisting the strut around - even in a vise the thing won't stay put (and a vise can damage the strut). Stand on the disc brake and whack it loose.