Why not put the car on a dolly?
Cuts the overall weight down significantly and really lowers the tongue weight.
You obviously DO NOT have the Mercedes Benz towing cross member (installed by the factory when
your Sprinter was assembled).
No such thing as a 3 series (316 with the 4 cylinder/7 speed)/2500 Sprinter with a 6000 lb towing capacity.
Adding a weight distribution hitch is a really bad idea.
WD hitches/load bars etc. work great on pick em up trucks and SUVs that have a fore and aft frame to "distribute"
the weight forward. Unfortunately Sprinters have sheet metal box beams to support the uni-body, instead of actual frames.
If you use a dolly your OM-651 4 cylinder engine and 7G-Tronic 7 speed transmission will have no problems if you can keep the
weight down around 5,000 lbs. and the tongue weight ~ 500 lbs..
I've towed a 5,000 + cargo trailer extensively with the 4 cylinder/7 speed and it did better than the V6/5speeds I had in the
past, but the fuel mileage suffered with a GCVW of 12,150 lbs. on a 2014 516 series (3500) with DRW and the 4.187 rear axle
ratio.
Hope this helps,
Roger