Sounds like the reason for the deformation is one of the "vagaries of construction." Probably the original and first universal joint was constructed and the fit was correct (I can see 0.010 free play of the universal yoke under the washer, although it could be zero)
I have seen an original "cupped" washer on disassembly which would describe the long term effect of what you describe.
Replacement universals AND transmission output shafts have been made which may vary from the original design incrementally - it may even be an "accumulated intolerance" which is when one part is made at one end of it's size range and the other is made at the other end of its range - and the two parts each meet the original design - but the two combined together do not.
For you the solution MAY be to simply "accept" the bending and "tighten it home" OR it may be a matter of putting a smaller diameter washer underneath the large washer to achieve no more than 0.010 free play.
The point of the washer IS to make the universal one with the transmission - mostly for ease of assembly but certainly as a matter of "locating" the universal so it doesn't drift backwards and cut into the universal joint hemisphere (there is not a corresponding restraint to the axle propeller shaft.)
Also, the universal and bolt/washer "binds" the rear transmission shaft and locates the transmission output shaft properly relative to the bearing.
Joe K
