Lower unit pressure?

[Quill]

Just changed the lower unit oil, question is, it's 30' outside, the oil is cold, when it warms up, from outside temp or running it, will the pressure if any hurt the seals? I'm asking because, when I changed it this summer I noticed that when I took the screws out that it had pressure. Probably a dumb question, but someone had to ask it.
Thanks Quill

[Trailerguy]

Your seals are held against the shaft by a simple spring, while you might see a little diference in "pressure" they will equalize on there own.