Cheers for the replies guys!
Right, I have cleaned the tip a little (I'm using acetone, but wasn't sure of the suitability re adhesives(?), so didn't get too carried away!) I found a little crappy microscope at home, and there seems to be a few deposits on the tip, especially on the trailing edge, as expected.
Sound is not a lot different, although when comparing some different vinyl, it's more obvious on one side of my Kate Bush Hounds of Love, so I'm starting to suspect a particularly duff LP rather than the Beogram, although the sibilants are still a bit more -sh than -ss if you concentrate hard enough :-(
The suspension on the cartridge itself is more "drooping" than I would expect (almost resting on the bottom edge of the cantilever orifice) I presume this shouldn't be so low? For this reason I am running the tracking force at ~2g.