Viggen Oil Consumption

I just test drove a 2002 Viggen that I'm looking to buy that has 36K
miles on it. Everything checked out fine, except when I checked the
oil level on the dipstick it wasn't registering. The owner had an
extra quart, and when we put it in it went to the top of the range, so
it looks like it was exactly a quart low. What could cause this? The
owner was very reasonable, and understands that I would want to get
this checked out. He is getting me in touch with his dealer to go over
all the service records as a first step. I'd really appreciate any
thoughts that other Viggen owners have on this? Have you had issues
with engines consuming oil at 36K miles? Thanks for your help.