Hard time with a HP 5385A with a repaired board

[pizzigri]

Hello everyone!
I finally received a HP5385A counter from an eBay seller located in Israel, I believe these were used by some military unit. The counter was described as “perfectly working” and the price was right, about 100 $  - although it actually more than doubled with postage and custom taxes by the time it reached me.
However, the counter has a hard time reading low level signals, so I tried to look for the problem, and I found a rather sloppily made repair on th board. R2, a 51.1 Ohm 1% resistor, that from the diagram I imagine being the internal terminator, somehow burned and was replaced with a part that I am not very familiar with a Vishay RLR/C military metal film resistor of the correct value, see images. The two resistors (R3 and R1) at its sides are badly scorched as is a small capacitor (C1), which have been left on the board. Also, lots of black flux caked on the board. There’s also signs of an IC replaced, U6, a Harris 1858 (wonder what that is).
So my question is:
The problem I see reading a frequency below the 3-4V level, can it be caused by this resistor?
Should I replace the two resistors around R2 and the capacitor?
Can the black flux burned frp! cause a problem?
There are other things, but those I can cope with, like a broken off rear BNC for the ref input.
Edited to modify after some research.
Thank you guys!

[Grandchuck]

I would clean the board.  You could test the adjacent resistors but they are probably OK.

If the input signal was large enough to cook the termination resistor it probably also damaged a solid state device down the signal chain.  Check the schematic to see which devices are close to the input connector and check them.

[Grandchuck]

CR6, CR7, Q2 could be damaged.

[pizzigri]

Ok! Cleaned the board, and will check the components today... there was a huge amount of crud, used a whole glass worth of 99.9% ethyl alcohol. The BNC connectors were also very dirty inside with black stuff (?) in them.

[pizzigri]

Welll.... it works
The internal TCXO is off by 2.5 hz vs my gpsdo and drifts too, but that will be taken care of with Miti’s ocxo board for this counter.
So the gunk actually created the problem??? I didn’t do anything else but clean it. Both diodes tested good (0.725V) and the rest too so after the clean up i reassembled the thing and firef it up.
Nice! Thank you