Originally Posted by moar
Are you sure they aren't on the key?
Spark plugs on my car aren't on the CBS but they are a servicable item, they are done every 3 oil changes which works around every 60k.
I imagine the glowplugs are the same ...
Glowplugs are definitely not a service item, and don't have a "useful life". They should last for as long as the car - after all, they are only used on start-up, unlike spark plugs which spark (and therefore erode) all the time.
I'd go with JonnySi's diagnosis