Well I'm not sure if a gorilla was responsible for the burnt resistors being lower than 100kΩ, as I discovered the very first batch of HP 5325A's (prefix 820) came with a 82Ω resistor for R3, but this counter is a later 844 prefix and the input amplifier boards have no space for the capacitor C20 that is in parallel with the 100kΩ. I wouldn't normally do this but I decided to modify both boards to match the 844 prefix manual, i.e. how it should have left the factory.
First I had to strip all the components from the burnt areas & clean the carbonised remains away, some Araldite was needed to fill in where one board was damaged.
The components were all tested, one Zener diode had failed, testing the remaining ones I have decided a 3.3V Zener matches the spec of the rest of them (approx 3.8V at 10mA), one of those has been temporarily fitted & I have ordered a couple of the original 3.83V part as they weren't too expensive (part no. 1902-3059).
I replaced a couple of the resistors that had faded markings, fitted the 100kΩ for R3 and a 1000pF capacitor on the rear of the boards, I also added a link on the back to properly repair a damaged track that previously had a bit of IC leg bodged on.
Both boards tested OK on all attenuator settings, guess I'm lucky the protection circuit did it's job & didn't EOL the dual FET.
David