300 diesel turbo tow car

I have a 1998 300 turbo diesel car and wish to tow a trailer weighting about 1800 kilos. 3600 lbs. I am told that when towing at or near to maximum manufacturer weight there is a modification which should be made involving a large oil/radiator cooler. The local main agent denies knowledge of this and I have not been able to get advice from Mercedes Benz UK. Has anyone heard of such a modification and what is involved in it?

Thanks