New user

[Curlyrach]

Hi all
I have a Rolex Airking which I bought secondhand in 2011. I have read about Patina, but around where digit 3 and 4 would be, I have some yellowing. Prior to putting this post up I posted it on a Facebook site and suggestions for the issue were : a watch maker has been sloppy and left a little oil....or potential zinc oxide and or perhaps moisture. I wondered if anyone else had any thoughts or had seen it before ? Its a 1990 14000 . I bought it from a reputable dealer at the time who stated it had just been serviced ( but I doubt now it would have been at Rolex). However it occurred after I had it.I stopped wearing it about 4 years ago but I want to start wearing it again but it irritates be and id like to get it sorted out if possible. Many thanks in advance.
Rach