I have a good friend (Canadian, Eh?) who is about to close a deal on Boler that has been painted, (like this !!!). He is asking me and I in turn am asking any Boler owners in our 'Egg Salad" where one should/might find the regi number.
I suggested he simply ask the owner to SHOW it to him on the trailer and to verify that number with the number he will have on the paperwork....
I have been told the you can find it on the axel. And durring my restoration, that's where mine was.
But on some bolers, it was mounted in other locations. Mine was on an aluminum plate, 1 inch by 1 1/2 inch. Unfortionatly, after 30 years on the road, that aluminum plate was rusty and worn. I could not read it. I lucked out, the seller of mine had the spec sheet that is usually posted on a peice of paper inside a cabinet door.
Hope this helps,