I'd recommend paying a visit to Golden Landmark Shopping Centre (look for Precision Watch Enterprise and Chuan Watch) and Far East Shopping Centre (HJWatch and Monster Time).
Paul at Precision Watch had two 6542's (one genuine bakelite, the other tropical), a 1655, a red 1680, a 5512 and six vintage tudor chronos. Chuan has many preowned pieces from other manufactures, HJ has a huge selection of preowned Rolex but not many vintage and Monster Time is like a vintage boutique with some rare pieces (other manufactures as well) but on the pricey side.
You could also check Hobbylink at Far East Shopping Centre while u're there and the watch shop (look for Barry) at the VIP hotel along Balmoral Road. Passions at Funan Digital Mall also has a ton of high end vintage watches (including the owner's personal collection not for sale) including a UAE datejust if I remember correctly.