Since you are looking for opinions and recommendations, I'll offer mine - and if it differs from the others I mean no disrespect.

You should be smacked with fresh bamboo and hung upside down by your toes if you take your car to Jiffy Lube.

(Remember now, I mean no disrespect - this is just the opinion of one unimportant person.)

Seriously, the MB diesel transmissions are pretty easy to work on when it comes to fluid and filter changes.

My recommendation is to change the fluid and filters right away. While I do not use synthetic engine oil in my diesel because of soot, I will use synthetic transmission fluid at the first sign of flaring. In my case I had a flair from gear 3-4 in cold weather.

I feel that the filter change is very important. A partially clogged filter may have an impact on the ability of the hydraulic pump to deliver the right pressure, and would make shifting disfunctional.

I tried to find Mobil 1 synthetic transmission fluid, and could not, so I went with the Quaker State 4x4 synthetic. With that and a new filter, the shifting problem went away.

Most people driving Americans cars know nothing about transmission fluid and filter changes, and don't have that service performed. So, you should always do this service on any used car that comes your way.

And of course after this, you should consider changing the differential gear oil too. Mobil 1 synthetic gear oil is great for that.

So, don't go for transmission service yet. Your symptoms sound to me like neglected transmission maintenance.

Ken300D