You want your struts to be clean so that you can tell if they are leaking. If you have an oily strut it should be replaced, depending on economics ofcourse.
Macpherson struts are a hydraulic damper, and as such, are lubricated internally, including the top bush, by the damper fluid. All this is held in place by the top seal assembly.
As XS650 says, not a good idea to try to externally lube them.
As an example, no off road race shock is externally lubed, yet can survive the worst Africa can throw at them for two weeks during a Dakar Raid intact.
Some mountain bike forks have grease fittings for lubing the top bushes, but this is only because the seals used were utter crap.