I've got
valenti tails on my car, and they've been leak free. Hell, the first day I had them it rained, and I throught I might have an issue, but nope! All good!
Just make sure you buy through someone with a warranty, like Modbargains, so if you do have an issue for some reason, they get swapped out without issue.
as far as stock goes, its usually a gasket issue...but it sounds like you've just had bad luck with them since you've had multiple sets. Time for new haha