Hi David, had this issue a few times with these 3 cylinder engines (AWY's mainly). 100% its the rings.

Tell your customer that you'd done such a good job making the top end of his engine 'gas tight' that it has now highlighted a deficiency in his bottom end which you weren't to know about unless you had fully dismantled his engine the first time around $$$$$$ (obviously the clever #### may question why you never suggested this at the time of the rebuild, so tread carefully)

Our main line of work is cylinder head related and every single job we take on, we always suggest to the owner that the pistons are removed for inspection. 95% of them turn it down but at least my arse is covered.

Not 100% sure about the BMD's, but parts are available for the AWY's and can be rebuilt (even though VW say otherwise)PM me your reg no if you want me to check parts availability.

Russ