Dirty, having cap removed and treated with grease (5)
I believe the answer is:
oiled
'treated with grease' is the definition.
(to oil something is to treat it with oil or grease)
'dirty having cap removed' is the wordplay.
'dirty' becomes 'soiled' (soiled can mean dirty or stained).
'having cap removed' means to remove the first letter.
'soiled' with its initial letter taken off is 'OILED'.
'and' acts as a link.
(Other definitions for oiled that I've seen before include "Anointed" , "Besotted" , "wasted" , "Lubricated or drunk" , "as silk may be" .)