Which location exactly?

@MrChris
It is generally a corroded fixing that causes your problem, however this is not so in your case!

If possible in your situation and you have a sturdy bench and engineers vice the rounded off head could be put into the vice and turn the bracket, hopefully to release. Tighten/ untighten motion does sometimes help together with release fluid of some type.

The broken fixing, if flush with the surface may succumb to a removal tool as mentioned above if you are very fortunate. Most likely to be successful is to drill it out very carefully and accurately to the Minor diameter of the thread and then re tap it.

Fallback option if you're not precious is drill them out then re-tap, or use a helicoil kit.

You 'could' try an ester cleaner something like AutoRx or similar to free off the rings. I have read it is effective if you rigorously follow the instructions, but I admit I have never had to try it

Patience and heat are your friends here. I'd start with a good easing oil,   I use Plus Gas or I have heard Bulldog BDX is really good, also 50:50 acetone and ATF.  WD40 not so good. Give it time to work (days), and keep applying it . If you can apply heat, even moderate heat, that helps. Also if you can give a couple of sharp taps to the screw head it can help loosen corrosion.  But then you are into easy outs, left hand drill bits, Anglo Saxon vocabulary etc. If you can move it at all either way, work it to and fro, don't attempt to get it out in one go.

Quote from: jvanzyl on Yesterday at 13:18Cheers, yeah I don't think it's the arms.. just a bolt.

I have a few sets of bolts for the rear arms.

Quote from: Carolyn on Yesterday at 11:11Spray outer joints with plus gas.  Wire brush exposed threads.  Spray again.  Heat up till very hot with plumber's torch.  Crack loose.

Thanks - this would be my approach if I had more time.. having looked at the costs of replacements and how much time I have over the next week it looks like it's best to just let this place sort it.. I've had a good run doing everything else myself, I've just reached the end of energy right now.

Quote from: Call the midlife! on Yesterday at 12:14Joe has another set of rear arms for sale £175 or so, might be worth a look.

Cheers, yeah I don't think it's the arms.. just a bolt.

Current timeline is to get it back Monday or Tuesday next week and then putter about with it going in a straight line and finally rid myself of the air lock prior to dyno.

If you can access them then I've found a left hand drill bit to be quite effective, you just need it to bite into the steel and turn the screw rather than snap your wrist with the kickback.
And if it doesn't turn the screw you can go on to try an easy out bit in the hole.

So I've managed to snap a screw and get another one royally stuck while rounding the head on one of my new hard top brackets... The screws were in pretty tight too.

Any recommendations on the best way to get these out? I've tried YouTube but most videos have "5 best ways to extract screws" but I believe these are well and truly stuck and the YouTube videos don't seem to have my situation.

Quote from: jvanzyl on Yesterday at 11:00RRR have bumped session to next weekend  so I've rebooked trailer for that.

Took it down to local garage to get alignment done- they came back to say everything was way out. Front inner and out tie rods completely rusted and unable to adjust, and apparently one cross threaded bolt on the rear trailing arms... so grand total for replacing all is coming to £500... 
Was not anticipating this...

Joe has another set of rear arms for sale £175 or so, might be worth a look.