GMT Master Aviator -Red/ 40-45yrs old? HELP

[Oxford914]

I inherited this watch from my partner who died of a brain tumor.

There was no box or paperwork.

The crystal is scratched, minute hand lost it's enamel and the crown is missing. In good working condition otherwise.

I am considering repairing it


Can you give me some advice on what it should cost to repair.

Will it lose value if I don't use authentic Rolex parts?
It needs a new crystal, crown and enamel replaced on the minute hand.

Should only an authorized Rolex dealer make repairs?

Thank you for your help and wisdom.