How do I know when my Lyra Helikon is 'worn out' ?

I'd estimate near-10 years with average listening 2...3 hours per day.
You will recognize its half-life sonically with distorted highs. In this case you simply increase the pressure by quarter-gramm or higher(by-ear) and continue continue listening for the other half-life.
You can't just replace the stylus in MC cartridge since this is quite complicated "surgery".

Umm it's worn out now. Mine is to. We both need the new Titan.

Jonathon Carr has a few posts on Audioasylum in the vinyl section. (he's the maker/importer or something to that effect) Anyway, he makes a comment that says how you lower the stylus onto the record has a big impact on his cartridges life. Do a search there under jcarr I think...

PS...found the link for you

http://db.audioasylum.com/cgi/m.mpl?forum=vinyl&n=265884&highlight=jcarr&session=