I sold my 540i as I had it for 3 years. I hadn't put it for sale, but an old customer asked me about it and I had always planned on rotating the car I drive. The 540 is such a special car that I really can't think of enjoying anything else.
Right now the middle size MB is available at a price I can do better with in a year. Then prices on M5s should have dropped significantly.
As to the balancer, its my conception that all early 112/113 motors use the same balancer.
Bosch Master, ASE Master, L1
33 years MB technician