Trim fluid getting into the trim motor

"I recently replaced the tilt/

"I recently replaced the tilt/trim motor on my 1990 Mercury 115 hp with an aftermarket tilt/trim motor and pump assembly. It ran perfectly the day that I installed it. However, the next day, the motor started struggling. It wouldn't run smoothly. It would slow-down, then speed back up rapidly. It almost sounded like I had a bad electrical connection. I removed the motor and pump today and a bunch of trim fluid had gotten into the motor. I had heard that sometimes the O ring between the pump and motor can fail and cause this. I was told it was from overfilling the system, but the mercury service manual says that the proper level for trim fluid is that it should be visible when you remove the fill plug. If it isn't you should add more. So it seems that it should basically be impossible to overfill it.

Any ideas why this happends or what I can do to prevent it?

Also, do I need to take apart and clean out the entire system before putting the new pump and motor on, or am I okay to just drain and replace all of the fluid?"

did you buy a new seal then in

did you buy a new seal then install?

"The unit that I purchased cam

"The unit that I purchased came with seals and o-rings already on it. So I just put the unit in.

The part is just like the ARCO 6278 (http://www.iboats.com/mall/spe.8594A/dz.5004/view_id.185163.html), but it is made by some other company. There was a large o-ring seal between the pump and motor and then a very small one around the shaft that goes from the motor into the pump. That is where the fluid got into the motor."

The company shipped me a new t

The company shipped me a new trim motor and said that the seal failed because I overfilled the system. They said that you should fill the system with the trim down. That is completely opposite of what the mercury service manual states. Has anyone ever heard that before?

Found the answer. Apparently I

Found the answer. Apparently I overfilled the system because I filled it with the engine trimmed UP. The merchant who sold me the motor said that I must fill the system with the engine trimmed completely DOWN. I contacted Mercury customer support and they confirmed that. I guess I was confused because the merc service manual instructs you to check the trim fluid with the engine trimmed completely UP and add fluid if needed.

I will know better from know on....