Vauxhall Vectra staring problems - camshaft oe crankshaft sensor ? or flywheel ?

Hi. My 58 plate Vectra estate has been a brilliant car until I decided to sell it when things started to go wrong ! Developed starting problems when warm (morning start OK)which after changing everything else indicated by the ECU readout, my local Vauxhall dealer replaced the crankshaft sensor (ca. £400). Some improvement for a day or so but then reverted to same problem symptoms. Battery replaced and started seems to turn over fine, just reluctant to fire and start up. Now same dealer says due to play in flywheel also causing possible starter problems (estimated £1500+ to resolve) and just co-oincidence that it causes similar symptoms.
Has anyone experienced same problems ? Is the flywheel scenario convincing ? Must admit I suspected sensor or fuel supply causes and can't immediately understand flywheel relevance, but everything else checked and replaced where necessary. I don't trust co-incidences and this is an expensive repair for a relatively high-mileage (112,000) 58 plate car, especially coming on top of the previous bill !