No W126 has such a valve.

If you need to retract the rear caliper pistons you can just push them back in. A better idea would be to open the bleeder while you push them in so you're not forcing old fluid back through the ABS module.

-J

__________________
1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket

Tesla Model 3. 205,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.