Thanks fo the replies.
I took the lock completely apart about 1 year ago, the ONLY bit that jams is the plunger as grit jams between it and the outer body of the lock
Unfortunately I have to leave it right under a roof edge(garage) so that the crap off the roof goes over the rear of the car.
The inside is never seized only the above bits, seems when you push it in it drage more crap inside with each push, the seal is there and ok, just think I will have to keep it clean around there, by washing crap away each week.
Thanks for replies
tabetha