The Logic Off Topic list

Although I'm increasingly doing mixing inside of Logic, I still use an old
Mackie 1604 quite heavily.
I frequently get crackles and dropouts when using the Bus Inserts (which
are basically, stereo jacks).
I'm guessing that the contacts need a good clean - the cables have been
replaced several times, they're never moved about, yet the problem always
returns. Another giveaway - turning up the gain tends to stop the dropouts
(which would suggest to me poor conduction).

So - can anybody suggest a good way of cleaning these contacts, or do I
need to get the unit serviced?
A friend once told me of a jack shaped object (mildly abrasive) that you
inserted into the socket to clean the contacts. I've not been able to find
such a thing, but would apprecioate any input from soemone who can
recommend a way of improving/cleaning the contacts in my setup in any way.

Any advice much appreciated