I’ve Been investigating a 08 reg 105 with the oil light flickering on tick over ,the engine is otherwise fine ,the only pressure relief valve Daf have is in Ipswich which suggests they aren’t a problem/ don’t sell many ? But at £100 it’s cheaper than an oil pump at £900 ,other than checking the oil pressure can anyone shed any light on the job ? Thanks Dan .
It used to be a common issue …
The bearing in the centrifugal filter would fail,though the main culprit was the screw in the oil pump ,drop the sump ,a battle in itself ,it doesn’t like being removed boy does it stay in place …Then on the O/S of the oil pump there is a circular screw with some holes around the circumfrence that would generally unscrew,Also had the odd 1 where the strainer was loose
Thank you Norb ,brother has changed the relief valve oil and filters , problem solved apparently 
Punchy Dan:
Thank you Norb ,brother has changed the relief valve oil and filters , problem solved apparently
hopefully that is it ,but if not a rubber mallet on the front corners of the sump will be required