I had my Monovalve out a couple of times recently (81 300SD), so I was kinda cocky when I installed the new one from Phil. When the assembly came apart, I dropped one of the thin washers down below the valve. Retreived it with a magnet and was on my way.
Next morning I was half way on my 75 mile trip to work, and I smelled something burning. Couldn't be the big rigs brakes, they were too far ahead. Smelled like a ballast from a lamp. Then I looked at the temp gauge...and ....bam! PEGGED!!
To make a long story short...back at the house while the tow truck driver was making out the bill, I found the thick washer fell below the valve also. Thats what too big a hurry will get you.
One thing I had going for me was that the oil had been changed just 200 miles ago. I changed the oil (smelled burnt as h*ll). Drove it a couple of hundred miles and changed it again. I took a 1500 mile trip in it last week, seems to be OK. Will I ever learn?