I recently picked up an absolutely mint W-E Doric desk pen (in Cashmere, of all places) and was wondering what the correct sac size for it was. It has a #5 adjustable nib and the nipple appears to be slightly more than 1/4" across. I've seen conflicting info from several sources on which size sac to use: Richard Binder's website cites the proper size as 17 or 18 (not quite sure if my pen qualifies as a Doric or a Personal Point) while some other sites give the proper size as 22 (which seems way too big). On a similar note, should I use a regular latex sac or a silicone sac to protect the celluloid (it's a grey-black color and I am unsure if it is prone to discoloration)?
Thanks for the help!