I recently purchased a O to G conversion kit after realising that the kit supplied makes an O version.
On investigation of the package I found that abysmal "quality control" by Mamod had let the wheelsets pass with the paint from the back of the wheel spreading over the flange and in areas onto the tread.
Being 'high-quality Mamod black paint' it is extremely hard to remove.
The photo shows the trailing wheelset of the G and the O from the kitset which shows Mamod can do it properly.
Being on the other side of the world my reaction after expressing my disgust at Mamod to myself was to try and fix the problem. As I have been doing in using 600 Wet & Dry to finish mating moving surfaces. This in the end proved disasterous, probably contributed to by my less than expert lathe work which prompts me to mention the 'muck-metal' trhe wheels are made of .... so be warned and take care
I have had to replace the axle of the front wheelset after it jumped out of the lathe at me and was bent.