The covers do have a replaceable seal where they sit on the heads. The small "breather" cover at the top of each is sealed with a premium RTV sealant. Mercedes has their own product for this, about $20 for the tube. Chrysler did mine under warranty with black RTV and the left side at the oil fill cap was leaking within a couple months. I'll re-do with MB sealant, Chrysler service is terrible. Do not reuse the 5 small aluminum cap screws, replace with new from MB parts, about $12 for the 5.