I'm guessing that the bushings were not poly but whatever rubber is used now. Another guess or two is that were not preloaded from the side plus were a bit sloppy in the bore allowing them to "walk". That 15mm space sounds a bit large - in American, about 9/16". Myself, would have liked to have seen half of that, maximum, or even less, say 1/8" and with poly bushings, even closer. That 9/16" converts to less support where you need it the most ~ 35+% less. Mine on my '31 are continuous plus are well supported with some preload on the assembly - and so far have been just fine, but I do check them each time I have the car on jacks, JIC