Thank you to all for the different information and tips.
I have taken the chassis to work and they have cleaned it using an ultrasonic tank. It wasnt an IPA bath but it has come out clean with all the crud removed. Unfortunately I wasnt there to see being done and it has removed some of the outer rim wheel coating. Which is a bit un-sightly but hardly noticeable once on the track. On the positive side, with all the gearing and axles oiled with sewing machine oil and the motor cleaned and re-fitted, the engine now runs quite happily, if a bit noisy. The outcome for me is that IPA is safe to use if you choose to do so. The ultrasonic bath would have been better if I was able to supervise the use of and if I knew what solution they were using. Given a choice I would have used an IPA bath. So all in all I am happy with all the comments on this post and will refer to it on my next engine restoration.
To nearholmer and IKKS, I have searched vintage/collectables on this site but cannot find them. If you could direct me I will look it up. Thank you.
Alan