What I noticed with this P750 design they did not countersink (what I would do) but counterbored (pocketed) around the holes where the orings are squeezed in, in between two parts. And some of the orings (like the gauge oring) did not fit in the pocket but got cut on the edge and most likely it was installed dry as well....
Following that concept I would suggest take a common sense... a smaller ID for the shaft and bigger ID for the hole (the metal wil push back the rubber)... and keep the same cross section if possible. If still no available, take the next up cross section (and smaller ID of course) and you can fix the "thickness with a very fine sandpaper. When installing a silicon oring grease is a must with this thing, originally they lube it with some sort of oil....
A bottom line, you want to fill the oring pocket with a most rubber material it can swallow. +0.1 or 0.2 or 0.3 mm won't make a difference.
The #49 is thick, that one can take the extra squeeze,
#54 take the next larger cross section because you will actually screw it in the hole.
the file extension may be a strange to microsoft ppl)
