I do believe the mounts contain fluid, However when getting mine from the dealer I was fixated on the fact that the new mounts were twice as thick as my tired old ones.
I never shook the mounts to see if they were being fluid filled, could have left that for my former secretary.

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Gary
Experience is something you get, Just after you needed it....
'99 E300 295K, '83 300D 220K, '75 240D 185K sold
'80 MCI Bus Conv DD 6V92TA, w/4 cyl. Kubota diesel GenSet 12.5KW