i don't know if i mentioned it properly but it stopped popping the RCD and instead now just trips the breaker actually in the machine.
I think you probably did, but I've forgotten that bit. I can understand your thought process here.

just for reference if i did decide to do the same what motor did you end up replacing it with?
Hah, no, that's a special case. I needed to replace a NEMA34 sized BLDC motor with something that would fit the same space envelope, and give me an easy spindle-speed control (the original Sieg SX BLDC had a very fragile controller card [blown it up twice] that only supported a "speed up" / "speed down" control). In the end I plumped for a Chinese AC servo which gives me a stupidly easy speed control (simple step/dir with electronic gearing).

That's not necessarily a solution for all, but it got me the power/control I wanted into the cast-iron spindle-head enclosure on my SX2.7. Not particularly cheap (£261.11 all-in)... compared to a replacement BLDC controller card (£247.48... fragile as F.. and no easy speed control).