It's not exactly a cheap item so I guess it depends on 1.) how deep your pockets are and 2.) whether it actually needs to be replaced or not? Have you encountered low oil pressure? Is there oil coming through the seal and gasket or just the gasket? Both the gasket and crank seal can be replaced.
When I first got my 850 TDI I discovered 3 to 4 studs/screws missing from the sump and lower side of the oil pump...most probably due to vibrations and shear neglect. After a thorough de-greasing of the area, some Loctite applied to the old screw threads and the correct torque applied proved successful.
As the bottom pulley (TVD) needs to be removed anyways it's recommended to have a new diamond washer and crank screw to hand. The old screw can be re-used (
not recommended of course) so, if you go this route, don't angle tighten it as it's already stretched. Just apply a touch of light grade thread-lock and torque up to spec. but by all accounts fit a new diamond washer between the crank and TVD.
This UK company has a good deal of parts for this engine -
https://www.brickwerks.co.uk/t4-part...i-ajt-acv.html