For that amount of money it might be worth a trip to Gainesville. We could save you at least a grand. OR you could call Maik Tessman at German Motorcars there in Tampa and I bet he will offer similar savings.
My partner is about 4 months into trying some of that stopleak in his S420. So far it has at least drastically slowed the leak. The jury is still out on this repair in the technical forums I follow.
Bosch Master, ASE Master, L1
33 years MB technician