Glad that you decided to just fix the kite rather than trash it!
Valves materials have changed a lot since 2007. Most were made out of PU in the older generation kites and now they are more made out of PVC. The PU valves would yellow with time and I guess people did not like that... The issue with these PVC valves is that the welding proved to be difficult because manufacturers were trying to weld PU bladder material to PVC material. Some manufacturers started using plastic (adhesive) discs in between the valve flange and the bladders to help solve this problem. The issue is if the temperature required to melt this disc is too low, then high heat on the beach or in your car could cause the glue to melt. One of the reasons why valves started coming off. After some tweaking of the material properties, most manufacturers figured out the right chemistry.
On a chemistry level, PVC valves have plasticisers in the material to help keep the valves flexible. This is why you can have PVC as rigid as a water pipe and as flexible as a pool toy. These plasticizers tend to migrate into anything that is in contact with them. So for a PVC valve, if the adhesive that is holding it onto the bladder does not hold up well to plasticizers, the adhesive could eventually break down and the valve could come loose.
Hope this helps! I would like to hear more input from the manufacturers on this topic.
, we have been very successful using STORMSURE to fix leaky valves. This product tends to stick to most bladders and valves very well. Let me know if you ever need more repair products to help with your DIY repairs projects!