Had a GLC do the same around 70k and a specialist found it was just stale fluid and a drifted adaptation. After a drain and fill with the right spec and a relearn, it shifted like new. Ask what fluid they use and get the part number on the invoice.

Be careful with "quality parts" unless the quote lists brand and part numbers. Some independents fit budget pads and still charge close to dealer rates. Get two or three quotes from Al Quoz workshops and ask for a written warranty on parts and labour.

Honestly I'd be a bit wary of a seller who won't give you an hour for a $40k truck. Not saying he's dodgy, but if he walks over a PPI request that says something. Could always offer to cover a cab or meet him halfway at a shop near his office.

Mobile services cover DIFC well during business hours and most carry 55D23L in stock since it is a common size for popular Japanese SUVs in the UAE. Call ahead to confirm availability before they head over rather than assuming.