wrote:
Hi, my Moen Kitchen Sink leaks from the base of the swivelling spout,
but only when the tap is on.

http://members.shaw.ca/dave_too2/sink.jpg

This is rings, not the cartridge, right? I've replaced a bathtub
cartridge before, should this be something I am attempting?

Looks just like mine. I suspect, as you do, that it is the seals
around the base, not the cartridge. I'd probably take it apart and
clean it in case there are some jammed particals causing leak but I
suspect you will need new seals - Moen should have on line.

Frank