Took a closer look at the SE reservoir. There's a secondary cap around the filler cap. If you disconnect the rubber hoses and lift the secondary cap, the heating coils come right out. You shouldn't lose much coolant since the hoses are the highest point in the cooling system.

With all this discussion of how to remove the reservoir, it's interesting that I don't know how to clamp the SD reservoir. It sits snugly but otherwise unsecured between the battery and the outer firewall.

Sixto
91 300SE
81 300SD