How to remove plastic glue'd models?

I've recently bought a bunch of used Orks from ebay but as I've looked further at the models I've realised that the Nobs all have heavy choppa's instead of my preferred (and army list built) power klaw.

So I got some bits online but now I need something to remove the arm from the body. I've had a look online and there seems to be a bunch of conflicting views on what will "melt" the model and what won't!

So does anyone have any real idea on how to remove the arm without damaging the model too much? Or would any of you just advise to remove the hand clutching the heavy choppa' and just cut down the power klaw? If so how would I go about this?

Thanks,
Firstcape.