Does anyone have any tips on fixing leaking valves ? Unfortunately this brand don't have replacement valves

Work the ball in the valve with a WD 40 delivery tube flushing it with the can contents at the same time. Then dry it with compressed air and then push a little bit of silicon grease into the valve.
I have recovered a few of my fenders with that method.

Cheers jolene. The majoni and Dan bouy have a nice little push in brass valve that would respond to the WD40 treatment. These are more like the polyform units which I'm guessing are a rubber ducks bill arrangement, bit like the one in a anti siphon loop/ bend. & I can't seem to find a supplier of the polyform jobs. It's a shame these are good looking well constructed units, brand new but totally useless

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woko said..
Cheers jolene. The majoni and Dan bouy have a nice little push in brass valve that would respond to the WD40 treatment. These are more like the polyform units which I'm guessing are a rubber ducks bill arrangement, bit like the one in a anti siphon loop/ bend. & I can't seem to find a supplier of the polyform jobs. It's a shame these are good looking well constructed units, brand new but totally useless

If all is lost you could try the old green slime or whoosh,,, or a modern day equivalent " pump my ride" for those that putt from the rough .

Well that's torn it, I was poking around the valve with the recommended pump needle in an attempt to get some slime in, and the whole shebang is now in unretrieveably on the inside. These 15" round fenders are used for rafting up. The hole is 10mm guess I could poke some old rope in it or maybe expanda foam, any ideas ?

See if you can fit a tubeless car valve or a patch valve into it

Bean bag beans and seal hole watertight

The tubeless tyre valve trick would be good if it could, but the chances of the rubber / plastics being glue compatible might be a challenge, I have some puncture repair stuff I will see if it makes an impression on the fender. Craig66 the bag beans maybe a tedious but possible & out of the box enough to work ! I will keep it in mind. Cheers

Cut a slit to pour the beans in using a larger sized fuel funnel - if you're going to use a puncture repair kit anyway(or maybe one for pvc inflatables) - it's just a slightly bigger patch.
edit: You can also stitch the slit 2-4 stiches with light braided fishing line first. Not close to edges - maybe 5mm or more- bigger the better. Rub the glue into the braid and holes before applying the patch.