Here's my thinking: With these V11 getting some years on them, and the clutch slave NLA from Moto Guzzi, it is going to be a real benefit to have a source for seal replacement. Most likely, a seal replacement will keep the cylinder in service for a long, long time.
I have also not found a Grimeca rebuild kit for this specific application, although there are 30mm brake kits out there. I may have to score one of those and inspect the seals for applicability.
BTW, McMaster-Carr also refunded my money. For now, everyone involved is moving toward a reliable solution. Thanks, everyone, for the assistance and education!
I have emailed an EPDM seal supplier for a quote on the square section 3mm x 30mm seal. The round section outer seal looks to be 2mm x 30mm.