Many thanks Gold77 for your kind welcome and most considerate reply!

Unfortunately, the 1435 flight is not available using Avios; however, I check daily.

The Arrivals lounge or visit to London are wonderful suggestions. (Afterall, London is my favorite city, thanks to the British people.)

Based on my reading, we would be unable to use the T5 Lounges, just as you also point out (we are ticketed DFW-BUD).

Many thanks again for the kind reply.