Don't use it . fix the leak . Think you will find the cooling system on these is 4.5 litres .

As e&a/c says, don't use it, fix the leak. If Radweld can fix the leak, then think about what other parts of the cooling system it can and will block. I know lots of folk will use this and similar stuff to hide faults on cars they're flogging.

Used rad weld many times on the Caterham, radiators simply do not last with the vibration and harsh use it got on the track. Never had an issue with any blockages but the engine was rebuilt at a max every 2 years so unlikely to be an an issue.

Latterly I used K Seal, found it more effective but its not particularly cheap, about £12 a bottle.

Now with the car not used on the track and not getting a long thrashing instead of the expensive one off type radiators I decided to fit a VW Polo radiator. Calculations showed that despite being only a 2 row core and having theoretically less cooling the fact that it was a more modern 2 pass design with a bigger cooling area it actually had more cooling. Off e-bay a Nissens one cost me about £27, about 10% of the cost of a one off.

So whilst home bound during lock down I set to with enough alloy to make a new mount and enough hose to connect it temporarily. After a few days it was on and held water. When I eventually got it out on the road it ran at the exact same temp as previously (about 88 degrees) so very happy. Even on the hottest day of 2022 on a brisk run to Cadwell the temp was stable at 88 degrees.

So in my example I got a new rad for little more than the cost of 2 bottles of K Seal. And with the brackets made and hoses sourced should the rad fail its going to be a simple swap to another Polo rad for about £30, got a spare just in case.

Never tried them but there arealso those tablet things that are alleged to contain ginger root fibres - Barrs leak?- apparently approved by GM and known in the US auto trade as "Cadillac Aspirin"