Brakedwell,
You were around before my time; I lived in Al Ayn from '65 - '68 in a quasi-political role. The border was there, although open EXCEPT for, importantly, any form of military movements other than the TOS Squadron CO based in Fort Jahili, and the Oman Gendarmerie C+O based in Buraimi, and the DIO who lived in Al Ayn.
In my time there, the fort in Buraimi was used by the Wali as a seat of local government as well as his residence, and as far as I knew it always had been. The TOS used Fort Jahili, just outside Al Ayn (now absorbed into the city) and as far as I knew again, always had done so since they based a squadron in Al Ayn. Are you sure you were landing on the Buraimi strip, as opposed to the Al Ayn strip? To the RAF in Sharjah the whole area tended to be thought of as simply "Buraimi" or the "Buraimi Oasis" without differentiating much between the 9 separate villages that made up the settlement then, 3 of which were in the Sultanate, and 6 were in Abu Dhabi.
I mentioned the permission to land in Buraimi only because I used to have to go to see the Wali and ask for it when requested to do so, which was very infrequent. He would invariably leave the room to ask the Sultan on his SSB, while I sipped the usual 3 cups of coffee.
Things were very different while the fighting was going on in Jebel Akhdar, with the RAF and the TOS both involved, and this is when you were involved, I think.
Incidentally, a book called Eastern Arabian Frontiers was and remains the definitive history of the Buraimi Dispute.
BTW, the TOS would not agree that the Saudis were expelled by the forces of Abu Dhabi and Oman; it was the TOS (TOL then), formed largely for the purpose, that did it.