Front shocks 123 series

[roundthebenz]

I need to replace both front shocks on my 123 series, I have a spare used gas :? pair, they look nearly new, resistance is good both ways but they take a few minutes to return when fully compressed. Should I assume this is a bad thing?
Have been given conflicting advice and I cant remember how they are supposed to behave.

Any advice appreciated before I stick them on!