Maybe the 1 in front of the batch no under the grip is an inspectors mark?
I'm no expert, but there were a few changes made post war, which would narrow the age range down a bit. Handle serrations, barrel knurling, markings on body, trigger shape, oiling instruction, etc. Photos would help, as always.
Don't suppose it would do any harm to try some neatsfoot oil on the seal.
No doubt someone who knows much more than me will be along!
ATB
Bru
Webley Mk3 x2, Falcon & Junior rifles, HW35x2, AirSporter x2, Gold Star, Meteors x2, Diana 25. SMK B19, Webley Senior, Premier, Hurricane x 2, Tempest, Dan Wesson 8", Crosman 3576, Legends PO8.