To answer your question. I would use a CVC torque converter. It has the updates for cold weather. They are about $200 with a core. Get them at Whatever It Takes.

Torque Converters Distributors Page - Consolidated Vehicle Converters, Remanufacturing Torque Converters for Automatic Transmissions

I use them for all my 722.6 torque converters on all my rebuilds. I do S600/S500's

How many miles on the clock?

I would inspect the front of the bell housing where the pump mates-up. Should not be pitted/ scratched..

What engine does the E55 have?

I'd replace the rear stater bushing bearing. The front bearing can be replaced instead of buying the expensive pump. Sonnax makes the bearings for these 722.6's

Rear Pump Stator Bushing - 68915-01 - Sonnax

Pump Bushing - 68004-01 - Sonnax

How far have you gone into the transmission?

Martin