ORIGINAL: causeitflies
I can't remember what's in my Wren SS but I think I may have changed that plug once in two seasons.
Interestingly enough Wren will soon be offering some kind of new ceramic plug:
"NEW - Wren "Long Life" Power Plug - ceramic element - 5.5 volt operation - simply replace your existing glow plug for improved reliability - £40.00 each - available very soon - Watch this Space!!!"
http://wrenturbines.co.uk/