Update: I've taken out the PRV, it came out easily, so was not stuck!
See picture of old and replacement, tadpole from JED....plus a couple more

Questions...
1.Spring is slightly longer, is that ok to fit?
2. As the 'thimble' was free so probably not the issue, says i have to 'prime' the pump?

So......can I do that by pumping oil up the tube for the PRV? Its on a 45 degree upward incline so I'm thinking oil will run straight out unless i can seal the exit in some way?

Appreciate your collective thoughts?

PS Melvyn Rutter are out of stock on the oil gaskets, so dismantling the whole pump and using vaseline will have to wait for a while....

https://ibb.co/SX7M7Ygv
https://ibb.co/0yPPXzxx
https://ibb.co/j94B3MjB
https://ibb.co/b5R7jyPV