Here’s the engine plate. I think I read on another forum that the initial 15 may be a year reference for 1965. Does anyone know?

Hi and thanks for letting me join the forum. I’ve recently bought an old Thwaites dumper which I think is a nimbus model from the 1960s.It’s powered by a Petter PH1 engine and I’d appreciate some help with maintaining the engine. It’s a runner and starts fairly easily on the handcrank. I’ve no idea how regularly it was maintained before. My questions are, how old is the engine – serial number 151188 , and apart from changing the filters and engine oil (plus gearbox and diff) is there anything else I should do to assess or maintain the engine. Finally, I’m in the UK, what’s the best type of engine oil to use? Thanks Jim