Mercedes GL320 2007 - Stuck in Neutral

[Wheatsheaf]

It's my sister's car - she lives in Dubai, uses it during the UK summer and the car has resided with me since Aug 2025.

It sat on my drive, with the battery removed, for 3 months September - December 2025. During this time, the front driver's footwell filled with water due to a split in the sunroof drain tubes. I fixed the leak, thoroughly dried the car (including the Signal Acquisition Module - SAM - which sits in a cavity under the front seat along with the battery), reinstalled the battery and the SAM, and started the vehicle.

To my surprise it started and drove absolutely fine - for about 10 minutes.

I put the vehicle in Park and left it on my driveway with the engine running while I weeded the drive . To my dismay I found that instead of being in Park, it was stuck in Neutral - and it rolled gently downhill, knocking over my garden wall, before I was able to jump in and apply the handbrake, luckily only making it about a metre or so into the road. Not a scratch on the Mercedes though. PHEW!!! It took five fully grown men to push it back up the gentle slope onto my drive.

As per the title, it is stuck in Neutral. Attempting to engage Drive or Reverse does nothing at all. If I attempt to engage Park, a rhythmic "clack-clack-clack" noise emanates from somewhere under the car, and that's it. I can then select Neutral on the gear selector and the noise ceases.

I do not have access to any diagnostic tools. I have toured local garages and none of them are keen to take the job on. It is a particular unappealing job (I guess) because the vehicle cannot be driven.

I wonder if anyone could point me in the direction of a specialist in the Bristol area who is likely to be interested in investigating/fixing the issue. I am unsure whether the water ingress could be the root cause of the problem or not. It did drive OK for about 10 mins, so possibly not. Failing that, any help or clues you could give me would be appreciated. This does not seem to be a common problem.

It's a shame because the car is otherwise is in excellent condition with only 120,000 miles and is the ideal car for my sister to use over the summer with her family (hiring a car this size is extremely expensive!!)

Here's the aftermath. And thanks in advance.

Edited by Wheatsheaf on Tuesday 6th January 13:51

[donkmeister]

Suggest you ask in the Mercedes subforum - Mercedes specialists are fortunately plentiful and you'll usually get a recommendation.

Hindsight is 20:20 etc, but I'd suggest you work out how to use the parking brake too! Being a 2007 would yours have a pedal or a switch?

Merc drivers are habitually likely to rely on the gearbox parking pawl instead of using the parking brake. The Indy who looked after mine (nowhere near you I'm afraid!) had seen a lot of seized parking brakes from lack of use, and even trained his staff not to put them on when cars were in for service after having them seize on at the garage and having unpleasant conversations with customers about who's fault it was.