I just bought a '99 Miata as a cheap car to have fun with. The previous owner really knew nothing about cars. I know nothing about how this car was maintained. I inspected it pretty closely in person before buying. I looked in the oil fill hole with a flashlight and noted it didn't look too bad in there. Now I'm going through the car fixing the little things I found and giving it a more thorough once-over. The valve cover gasket was leaking. I took the cover off tonight to fix it and take a look at the timing belt. There was no paperwork or labels indicating the timing belt had ever been replaced. Overall, it looks like good news to me. This isn't the cleanest engine I've seen, but it's not the dirtiest, either. The timing belt also looks really good. It is pretty clear to me that it's been replaced and it sure looks to me like it hasn't been too long since it was replaced. The oil is pretty dark as it needs to be changed, but I don't see too much buildup beyond what's on the inside of the valve cover.