RB67 prism not-metered question

I just received an RB67 prism model 2 (ex+) from one of our favorite suppliers (for my Pro SD.) It looks great, but won't fit onto the camera. (The waistlevel finder detaches and attaches just fine.) I think the problem with this particular prism is that the rubber friction bumpers on the underside are stretched and starting to detach, so the fit is too tight onto the camera. It looks like a repair by Mamiya service would be aroud $150.

So, another option is to exchange for an original style prism and see if that works. Any advice on the fit, something I overlooked? Am I missing something going with the older style prism? Thanks.

It mounts just as the waistlevel finder does but I think the mod 2 does have a sliding lock that your waistlevel finder may or may not have, depending on its age. Other than that they mount the same.