I had to change the O/S rear radius arm bearings on my wife's Mk1 at the weekend. I did the other side a year ago and it was no problem but this one had the bolt well rusted in and no amount of hammering was going to knock it out.
With a long breaker bar I managed to get the bolt turning but it was still rusted into the bearing sleeve which just turned with it. I thought about cutting the ends of the bolt off but the head is just too inaccessible to get an angle grinder in there and there is no room to work a hacksaw. So I drilled into the head of the bolt, working up to a 13mm and then belted what was left with a cold chisel so that what was left of the head came clean off. I then put the nut back on the other end with a couple of thick washers under it and tightened it up to try and draw the bolt through. With a 4 foot length of tube on the end of the breaker bar the bolt gave a big crack and started to move. It was hard work for the first inch or so, increasing the size of the spacers as the bolt withdrew, but after it had come out about halfway the rest pulled out by hand. The bolt had about 2" of rust at the inboard end that had been holding it in. The new assembly went together with plenty of grease.
I just thought that anyone else who encounters this problem might be interested in how I did it.

I went to the fiat dealer, bought a new nut and bolt. with the new bolt as a punch to knock the old bolt out, and was careful not to distort/mash up the end of the new bolt getting the old one out. Sprayed what i could see of the old bolt with loads of WD40 and left over night to seep in. then i gived it a push with a mallet, (should have done the trick) but that didnt help so i saw through the bolt both sides of the arm that got it off..