The seat for the bike was in excellent condition (no rips, tears etc), only a little bit dirty. I dragged it indoors and applied some leather balm and scrubbed the dirt out. The results are entirely satisfactory.
The only issue is with some rust on the buckle on either side. I haven’t really made an effort to resolve that concerning myself more with the leather itself.
I may give the seat another going over to get some of the more stubborn bits out, but I think I can turn my attention elsewhere. As an added bonus I discovered the original owners manual in the compartment under the seat sealed in plastic.