There are a couple of gaskets that depending on how long ago they were pulled appart, sort of "glue" it to the body.
There is an inner and outer, inside the trunk and outside the trunk gasket that may be hardened and holding the bolts in place. you may try gently hammering at the studs to push them out, rubber mallet or something.
Even mine which I have pulled out get hung up on the inner one that I am afraid to try and remove. The gasket that is.
Ah but mine is a 440 model. My bet is the assembles are installed the same, but maybe not.
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