Look up a guide on youtube on how to change/check the fluid level on your specific year make and model I guarantee you’ll find something. If the fluid smells burnt or discolored you may need a fluid change. If it has never been changed, I would at least try that first. If he’s a good skilled and trusted mechanic he will most likely be right. If not, search around for someone who specializes in European cars, usually specialists will have a bit more insight and knowledge compared to someone who “specializes” in all makes and models.