This is always a concern, but I've bought many abandoned vehicles, some that sat over 20 years, and had no seal issues I can recall.
My current boat is a 2007 that was apparently never used, and was stored outdoors in Bullhead AZ which is a pretty harsh environment. I haven't put a lot of run time on it, but it's been around 9 months and no leaks so far. As a bonus, the owner parked it with the hull drains installed so the engine was mostly underwater. The high water mark was almost at the valve cover, when I got to it the water was at about mid cylinder area.