Oyster Perpetual Identification and Servicing

[HowieS]

We recently found a few watches tucked away in an old safe belonging to my father-in-law. (I have read the sticky posts)

I believe based on the documents this is an Oyster Perpetual Datejust Ref. 1625.
Can someone please confirm and add any other interesting information about the model?
I saw a few places saying Thunderbird?

It was purchased in 1976 in Singapore and still has the original receipt, box and documents, although everything is looking a bit tired.

There appears to be a few small chips in the glass and a build up of gunk.

What would you suggest regards cleaning and servicing based on the pictures?

Would you advise replacing the glass or keeping everything original?