Tilt & Trim trouble

[Kongfish]

I have a 1990 Mercury 175 outboard
The tilt/trim was working fine and then suddenly yesterday, The tilt/trim started acting a fool.
The tilt will motor will go both up or down but it does so, very slow and then it will stop after about 4 seconds. I will wait ten seconds or so & the tilt/trim will go up for 4 seconds and stop. It keeps doing this and also the area where the tilt speeds up normally,doesn't change speeds it just keeps going 4 seconds then it stops.
Does anyone have any ideas on what I should try to do or what is wrong.
Ps: also when the motor is going down, the motor bounces.

[Ski]

Check to see if the trim motor is flooded with water and rusting up. The bouncing sounds like it's low on fluid

[Kongfish]

Ok,
I will check that tomorrow. But let me ask you this.
What is the proper way to go about checking & adding the power tilt/trim fluid on a 1990 175hp Mercury ? Me stuffing that little 12 ounce bottle into the opening and getting what I can in there the best I can seems to not be the most effective way to add fluid to the tilt/trim, sonce the opening is sitting in a vertical position? I know to go up all the way and flip the engine prop rod up to keep the motor held up safely. But I don't get how to go about adding fluid, or even to correctly check the fluid level.
Also, how or should I drain all the fluid out to check for water in the tilt/trim motor?

[Kongfish]

Ok,
Here's what I have found.
The whole issue derived from the Plastic pressure release screw falling out. I have to assume the previous owner screwed it in and didn't comprehend the importance of the E-Clip.
I now have the problem of the part I bought to fix the problem won't screw into the correct slot. I got the part number for the replacement part from the Mercury catalog, and I know I am looking at the correct part from the correct trim I schematic.
My problem is that the part I have seems to be to longer than the depth of the whole it goes into.
I haven't ever seem the plastic screw with rings on it from my motor it was gone once I figured out I had a problem.
Can anyone tell me what the correct process is to install this part?

[Ski]

whats your serial number?