Picked up my first T25 earlier in the week, and subsequently spent my first evening under it with a snapped exhaust pipe

Anyway whilst i was under there i noticed the oil filter looked like it was off the ark (despite having a receipted service less than a year ago). So i plan to give it a full service for piece of mind if nothing else. However I do not know which engine i actually have?
I think i have narrowed it down to DH or GW code.
Its a 1.9 1985 with injection.
Is there anywhere it is stamped to i can ensure i buy the right service items. (also any recommendations for places to buy items..i usually just go to GSF and get Mann, bosch, beru stuff)
Thanks