Update: Well I got wrong info, there never was a spacer on front mount. In fact the tabs on the plastic spacer will not fit into mounting hole on the front mount.
I recently posted how I looked at the front diff. mounts and discovered that the foremost one had slightly distorted rubber mounts. What I did not realise was that some syncros have plastic spacers on those mounts too. Mine did not. A quick survey on the syncro and the vanagon mailing lists only returned one other owner (also an ’86 van) that did not have those spacers installed in the front mount. The parts catalogue shows none of the front diff. mounts having spacers, but do list them on the side, and 4 needed (4 would be enough for only the 2 rearmost mounts) You can see at least the rearmost ones with spacers in the Bentley manual. The part number is 251 199 399 , its the same plastic spacer that is found the transmission mount. I decided to try and make a spacer(s) and found a scrap of polyethylene cutting board that was big enough to make a reasonable copy. I just need to make another then install and see what difference it makes in the front diff. flange angle saga.
If there is anyone out there interested enough to have a look at their own syncro front diff front mount and report back presence or absence of spacer, I’d be very grateful.