The TXV may have been crossthreaded at the last installation and that's why it leaked? Are you putting in a new TXV? Check the threads on the line fittings as well.

Turn Counter Clockwise First Then ...
 

Oil the threads on the lines and in the expansion valve and turn your nuts counter clockwise by hand till you feel where the treads would catch and then give them a little tap on top of the line gently forcing the threads tightly together. Then gently wrench them clockwise to tighten them.

I just did a dash out changing the evaporator and expansion valve on my 1987 420 SEL and I know it’s a …, but be patient.

Connect the top two lines and the suction line on the bottom before tightening them. After those three are tight then do the line from the dehydrator since the bend on this line rests under the suction line.

And by the way you will need a set of crows feet to get them torque to specs!

Hope This Helps!

I bought a set of crows feet and thats the only way I got the stupid thing off. I stopped yesterday so today I would do a good job and not rush it.

Good thinking, Don't get frustrated, Let the oil part go unless you did the dryer too. I also think you might check for crossed threads, As said. If you put a dryer in then add 1 or 2 oz.

i got the new expansion valve in tonight and added a small amount of oil as i changed the dryer about a month ago and didn't add any. i pray to the big guy in the sky that i did a good job because i don't want to ever ever do it again. tomorrow i have it vacuumed and i will recharge it and see how it goes. wish me luck and thanks for all your inputs.