Just as a followup...
Car still runs great and has all the power it should, but does not start immediately if it has been sitting off for a while. I had my wife try turning the key on and off a couple of times before starting it after it had sat and it did fire right up then, so it appears that the fuel pressure is bleeding off over time.
My suspicion is that the replacement Viton #138 O-ring I put in is just a whisker smaller in cross-section than the (probably metric) original and it is allowing gas to weep past when the pump is off. The Viton is a slightly higher durometer than Buna, at 75 vs 70 and that may not be helping matters, especially with the cold temps we have been having.
I'm inclined to leave it alone for the time being and try to source a replacement cap. I kept the original O-ring and will probably put it back if I can find a cap - I really don't want to mess with the cracked one I have now if I can help it.
I searched car-part.com for a fuel pump and they didn't have any listings whatsoever.
Found a couple of pumps listed on eBay for $90 in a junkyard in VT, about a 2 hour drive from me. They did not have actual pictures of the pumps, and the listing was somewhat unclear so I sent them an E-mail asking if it was just the fuel pump itself or the entire assembly via their listed contact address the day before yesterday but have not heard any response back from them as of yet.
Next best choice I have found is from Advance Auto Parts,
at $338.09. They currently have a 15% off promotion going on so that would bring it down to about $288. Free shipping, too.
Not sure what I'm going to do yet - waiting to see if I hear back from the junkyard. My wife relies on the car for work so uptime is very important.