Bosch Platinum plugs

Same thing happening to our 440. Lots of missing during cruise. No real missing during load acceleration. Plugs were totally covered with brown plastic looking crap.
I generally think minute electrode plugs will foul over quickly on old designed engines.
The plugs (ngk v groove) were probably fouled by the fuel additive I was running all the time. Plugs had about 2k on them. Also the motor is 37 years old and only has 25k on it, so rings may be weak. Also, the plug boots on the plugs were cracked to hell. Here is what I did. I scraped the oxidation off the pins inside the dist cap, scraped the rotor contacts, put autolite coppers in the motor, cut and re routed the plug wires with some autozone plastic plug wire clips. New plug wire boots on the plug end of the plug wire. Runs perfect.