I have received the 912/356 distributor rebuild kit from Stoddards. It has a new Phenolic washer in the kit. there are also several shim washer that I will use to reduce shaft end play... IF I knew what the spec was... ANYONE???
Parts in
red rectangle are unknown to me from taking 2 SC distributors apart. Parts in
green rectangle are the same as parts on my distributors.
Red circle is my broken washer;
green circle is the replacement:
So good news for me

I might just order a few more of these kits for spares. Usable parts:
- 1 Phenolic washer
- 1x 0.07mm shim washer
- 2x 0.09mm shim washers
- 3x 0.19mm shim washers
- 3x 0.28mm shim washers
- 2 'E' clips (clip the weights on the weight shafts)
- 2 replacement felts
The shim washers are the same as:
- the small washer at the end of the shaft between the gear and phenolic washer
- the small washer above the phenolic washer as the shaft enters the distributor cup
KTL:
Measuring the new washer and comparing on the link you posted I would be happy to go with a 1/2" Low-Friction and Chemical-Resistant UHMW Polyethylene ID - 0.515" OD - 0.885". The ID of the new washer is 0.505" and the OD is 0.808". the only concern is the thickness being ~0.02"+ greater. New washer is 0.030" thick. It could be entirely possible to fit one of these with different shims and get a perfectly workable solution.
Best regards,
Michael
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Michael 
'82 Euro SC 'Track Rat' 22/29 Hollows, 22/22 Tarrets, Full ERPB F/R, Rennline Tri Brace, Glass bumpers, Pro 2000's, 5 pts, blah blah blah
'13 Cayenne GTS