"Gala Week" seems to be readily available on Amazon or Abebooks (in used copy anyway). Since cost is peanuts I decided to order it. Our library system has it only as audio book. Review on Amazon intrigued me:
"The book lived up to all expectations. Well written in the Yorkshire accent the book chronicles the week of her birthday and his idea of a gift that was unusual. Combine this with Seymour's gala exploits and the result is a strong, humorous and warm story typical of Summer wine and its characters."
Does not say who "she" is.
Also looked at "The Moonbather" - also readily available. That review was more complete:
"If you want to spend some time with Cleggy, Seymour and Compo, with appearances by Howard, Marina, and Nora Batty, you've got to pick up the Moonbather! Written by Roy Clarke himself, reading this feels just like watching an extended episode of Summer Wine! I could practically hear Clegg's voice, his mild tone occasionally filling with humor, as I read his dialog. If you're a fan of the later episodes, you may be disappointed not to find Truly, Entwhistle and others, but even so this is a hilarious read!
The Plot: Seymour intends to court a `young lady' (of around forty), but thinks his place is too far away. He insists on using Clegg's place, and when an angry Compo shows up at the party, along with a streaker the whole village (led by the lady's policeman fiancée) is after, things get a bit complicated and very funny!"
Interesting both books are from the Seymour era.