You can source a new part here:
https://www.digikey.co.nz/short/p7h428mqI've repaired a few of these boards in the past with the same problems caused by battery corrosion. There can often be open circuit tracks under the 74F74 as well, so I'd recommending removing the IC and carefully checking all tracks and vias underneath. Since the IC has been subject to corrosion, it should be replaced even if it's working. As I recall, it's used as a clock divider, so with a 50MHz oscillator, you should expect to see 25MHz on one of the two outputs. I don't remember if only one or both elements of the flip-flop IC are used, though from looking at the 74F74 datasheet and connecting tracks on the PCB, it's not too hard to work out how the circuit operates.
I can also repair the board for you if the above detail is outside what you're comfortable with.
http://amiga.serveftp.net
