Mr. Bill,

If your 90 SE is anything like my 91 SE, you'll have to move the diagnostic port out of the way (2 screws behind the transmission dipstick) and a 1/2" OD coolant hose just above the monovalve. Go easy on the hose because it's connected to a plastic fitting.

You don't have to disconnect the monovalve wires or any wires for that matter.

The sequence of washers on my car from top to bottom is small thick washer, wave washer (part of kit), small thin washer, big washer.

Sixto
91 300SE
81 300SD