A couple of things.

Don't use a multi meter to check the spark plug wires while the key is on or when cranking the engine. Voltage here is upwards of 20 KV ( that is 20,000 Volts ) under the right conditions.

There is a gap between the rotor tip and distributor cap towers so you won't see continuity between these two. The cap won't be damaged by a cut coil to cap wire so the problem lies elseware.

You will need some sort of trouble shooting information from a manual. This system should be the same as the same year 300SL as the engines are the same.