Hi Chrisp,
if it is an Evektor Eurostar i strongly recommend you to check the flex spiral tube part of the exhaust manifold against cracks before buying, i experienced such cracks which burst open at 350 hrs (5 years),
apart from that all rubber parts of the Rotax must be replaced every 5 years, including the mechanical fuel pump
Only on certified engines (I dont know any eurostars with CAA airworthiness certificates BTW)
Permit aircraft almost always (99.99%) use the uncertified engine and run on condition
(would be a bit daft not to really)