Air getting into trim and tilt

I am having a constant issue of air getting into the PTT. I can’t see a leak, out of the piston seals, but air is getting in there somewhere and fluid is leaking out somewhere. When bleeding the system, I can never get all the air out and I have to add a little bit to resevoir every time. Any ideas? I am planning on replacing the seals, but I was looking for any other suggestions on what I should look for when I have the PTT apart. This for a 2000 2 stroke yamaha 115.

you have an internal issue
the fluid is getting aereated by the pump

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That makes perfect sense ChrisV. Should I be looking at replacing the gear pump assembly?