Well, we have taken two camping trips since the repair.
On the first, we completely filled the grey tank over 5 days. At the end, it
started to drip soapy water,
so either there is another leak I missed, or the Vulkem coated patch is leaking. Nothing happened until the tank was full.
Time to punt. I went to the local RV dealer and picked up a 30 gallon portable waste tank. One more thing to carry in the truck. It has the advantage that we will no longer be limited by the grey tank when staying for many days. Most of the campgrounds (state/federal) we stay in have electricity, but no sewer or water connection at the site. I can always carry 7 gallons of fresh water from the nearby spigot to refill the fresh tank, but hitching up to dump the grey is a lot of work. The "blue boy" style tank can just be hooked up to the hitch on the truck for an aromatic trip
to the dump station.