Yamaha 225 tilt trim issue

I am having issues with the tilt trim on my bass boat. I had a leak around the seals/cylinder which i replaced. Shortly after replacing these parts the trim motor went out. I replaced it and then the second motor quit as well. I noticed that hydraulic fluid was getting inside of the electrical motor causing it to quit working. Can anyone tell me why hydraulic fluid is getting inside of the electrical motor? I understand that there is no pressure to cause this. Could i be over-filling the lines with hydraulic fluid and if so, what is the recommended amount of fluid for this tilt trim? Thanks in advance