Had a similar prob earlier this year, in all the snow/ice etc. Decided to change glowplugs, as first point of call.
If you are going to do them, do all 6 together, else you end up repeatedly taking off the manifold et al to get to them.
£16 each??? My local dealer wanted £9.50 + VAT each, but got some from E-Gay (6 brand new NGK, boxed, unopened) for £29.50 inc P&P.
job takes about an hour + to do them all, and you need a deep reach 12mm socket..
Hope this helps.
Right quick update
Not sure how to do in an hour seemed to take me a while lomger but all changed today and starting
much better would not fancy doing with intake manifold in place far to cramped, anyway job done thanks to all for all your help and input ,having looked at the old ones three are not reading so i guess goosed and three are reading 1.1 on meter but all very pitted and charred so needed doing.
thanks again.
andy