Most of the ones I've had on various pieces of equipment constantly leak. Even the new replacement ones are not very good and end up leaking in short order.
Here's my $ .02 on it: The older ones that every old tractor used to have (we're talking tractors that have 50-70 years old) work great. They very seldom leaked and did their job.
Then foreign manufacturing came into the equation and now just about any new one is junk. The added alcohol probably doesn't help matters either.