Real Steel in Uxbridge is one of the better sources of Holley parts in the U.K. They were also the only source of 390cfm of base plates / throttle spindle assembly when I needed one.
I bought my low mileage V8 with a Holley on top about 30 years ago and there are perishable items, hence their rebuild kits and gaskets. Its easy to work on and almost fit and forget. Here's what I've dealt with.......
The accelerator pump has a rubber diaphragm. It perishes with age but also rips prematurely if the lever arm clearance is set incorrectly. This dumped fuel on the inlet manifold every time I pressed the gas pedal. I was driving through central London in rush hour at the time...
Wear in the throttle spindles / base plate was another issue. Fuel was leaking out by the throttle lever. It had basically worn out. The carb was probably older than the engine. As above only Real Steel in the U.K. carried them as the carb isn't that popular in its homeland as its small by comparison to US V8's. I had to wait several weeks for their container shipment to arrive from the US, otherwise they could have air freighted one for an extra £60 to £80.
The fibre washers under the float height adjustment screws perish with age, especially if they're adjusted when old and fall apart. These are the large brass screws on top of the float bowls. Not a true leak but one to watch.
As Ed mentioned, the O rings inside the tube connecting the 2 fuel bowls can weep, not happened on mine yet.
I'd also have a look at your fuel line to the carb. I had some "quality" stainless steel braided line which perished after a couple of years. There was a stink of petrol but no puddles as it evaporated amongst the braiding before dripping. I couldn't see any liquid but by running my hand along the line I felt a cold spot where it was evaporating. Maybe due to ethanol in petrol, maybe not.
I've not had the fuel bowl gaskets fail on mine as yet. However when I replaced the base plate I rebuilt the carb and replaced them as a precaution. Putting them in a jar of fresh fuel didn't rejuvenate them. I'd nip up the 4 screws on each fuel bowl on yours anyway to check they're not loose.
As per Manny, Bobs website is the best online resource out there, followed by numerous videos on the Holley website itself. Run the engine whilst the car's stationery, blip the throttle to activate the accelerator pump. Let us know what you find....