Well that’s why I’ll go to the dedicated Merc place on Friday. I’m told they are enthusiasts and very good so I’ll accept their opinion and experience.
Are you taking it to an independent garage or back to the selling dealer?
If the former, are the independent garage tasked with obtaining a diagnosis?
If it is going to an indie (again) have you actually contacted the selling dealer yet? You should at least call them – just say ‘I don’t think the gearbox is right, hasn’t been since day 1 but due to work/holiday this is the first chance I’ve had to look at it properly. I’ve found a good indie with dealer level diagnostics. Are you ok for me to get them to take a look or should I bring it to you?’
The path you’re setting off on is likely to result in all costs landing squarely at your door. If it is borked, and the dealer gets a whiff of third party involvement before they’ve been given the chance to take a look, they are quite likely to tell you to foxtrot oscar.
However, you might find they are more than happy for an indie to diagnose/advise on the issues. To have the full weight of your consumer rights behind you, the seller must be given the opportunity to repair.