Speedmaster Bezels

I have noticed two sizes of replacement bezels for a 145.012-67, I've seen 37 and 39. I've been trying to replace my lost bezel and twice the bezel could not be put on the watch by reputable watch repairmen. Should I be looking at a 39. Can someone enlighten me on the correct size. Of course, I purchased the least expensive ones hoping to get a deal. The costs go from double digit dollars to 4 digit for authentically old ones. who can I trust?