Towing load > 2,0 t at MERCEDES 308 D, 79 hp possible ?

Hello T1 driver, I drive a 308 D (602) long+high, with 79 hp and a zGG of 3,200 kg. The usual 2.0 t are registered as trailer load. I would like to register a higher trailer load now. The trailer coupling itself “can” according to D-value calculation 2.5 t. In the past this was easy: you went to the TÜV, had a limitation of the climbing capacity to 8% and had its higher trailer load. According to GTÜ examiner that is no longer enough. However, I have been waiting for this for 4 weeks, and it is questionable whether MERCEDES will ever come from it. Then there is the possibility of an expert report from companies specializing in trailer load increases (SK, Scholz, MAD … and how they all are called). However, since my van was placed on the market with Blanko letter and by a single purchase (in the papers the TSN is “encumbered”, all companies have canceled. Although the car is identical to other 3 08 D is, because of “000000” it is considered to be “not available in our databases”. Then there is the possibility of a single acceptance at a technical inspection center (TÜV in the old, DEKRA in the new federal states). That is now my last hope. I would like to explain to the examiner that there are other 308D with increased trailer load. So I ask: Does anyone drive a 308 D (type 602) with more than 2.0 t registered trailer load? Greetings Jürgen