Most scopes don't get a lot of use anyway so if it looks in good condition it probably is. It is easy to adjust any play in the mount drives trains if needed.
http://www.astro-baby.com/heq5-rebuild/heq5-m1.htm
Second hand heq5 pros go for around $700 and I believe a belt mod costs around $100, 18 mths is practically new anyway. If the price is right it will sell quick.