U joint it

When replacing your u joint, does it matter which direction the grease nipple is facing? should researched the topic before replacing u joints and bearing. I've never owned a truck before so I asked a buddy of mine how to replace u joints and Center bearing. (He's a mechanic) after our brief discussion on the phone I immediately went to work. Everything he said was right, but perhaps he forgot to mention a few minor details?
Can't get a hold of him, he went to the mountains with his family for a vacation.
Again: thank you in advance for your collective knowledge and your time.
All recommendations are acceptable as long as there is no mention of the Flux Capacitor

 

I’d say it doesn’t matter as long as you can grease the nipple once its installed. You’ll need to access the zerk in the future every 5-10 thousand miles.

 

Yeah that's what I figured, i didn't see a little groove or any type of indicator telling me to place the zerk in a certain spot.
I'm asking because this happened to me yesterday.
Bearing cap decided to hit the EJECT button while I was on the freeway.
Scared the hell outta me. I have since replaced the Joint and Everything seems ok but I can't seem to seat the last snap ring in place.
Idk what it is? I was extremely careful this time around and triple checked as I was installing the new caps. No bearings fell outta place 100% certain on this. I'm not a pro or a seasoned truck owner like you guys on here but I know for a fact that all snap rings should be seated in their little groves.
Everything is cleaned out, groves, old grease, road dirt and metal burs.
I can't seem to figure out what the hell is going on. Spent 2 hours last night figuring it out. Drive shaft went back in the same way it came out. Marked every

 

I’m sure what to tell you at this point as it seems you’ve check all the boxes. Maybe the u-joint is too big? Try thinning the snap ring down as a last resort depending on how tight the tolerance is.

 

I've been keeping an eye on it. So far so good. No "wobble of death" while driving.
I got to thinkin, that maybe since they come pre packed with grease its difficult to seat the last one because you can't compress a liquid? (Idk if grease qualifies as a liquid)
It has to do with Pascal' law or Bernoulli's law or whichever of the two.
Like I said so far so good.

 

99.9% of the time... if a U-joint cap wont fully seat... it's because one of the needle bearings fell out of rotation and stuck in the bottom of the cap.
They don't seal well enough to hydro-lock as you describe.