If the reservoir bottle is empty that could indicate a problem.
As said the only way to tell is to have it checked out.
first is to remove the drive from the gimbal housing,
then inspect the U joint bellows for gear oil.
if gear oil is present then most likely you have a upper carrier seal leak, (common with use and age)
The specific way to determine this is to empty the drive of oil, the pressure check the drive to ~ 15 psi. It should hold this pressure for 2 minutes. (drive must be off boat)
This actually should be done anyway as the boat is new to you. You want to be sure everything is in good condition.
I pressure check every outdrive I service regardless.
A side note, when a drive is emptied and refilled, if the reservoir is full to start, once the drive runs the reservoir will empty almost 3/4 of the way. This is the nature of the system. Once emptied refill to line. Then this should stay this way for ever unless there is a leak.
Running a outdrive with an empty reservoir is a NO NO........if the gear oil is leaking out past a seal then the UPPER gear case will be starving for gear oil and the bearings and gears will get ruined.
As this boat is new to you and you are unsure, I would either bring it to a trusted boat tech or if you have a mobile tech available see if he can come to you.
If a mobile guy can come to you then you can observe what he is doing and possibly ask some questions.
At least I never minded answering questions..............
We here can only answer so much. The real answers will be seen first hand if properly tested by someone who understands what they are doing.
Good luck!