As with anything, time will tell. They are made of good, thick rubber and fit my pumps very snugly. I have to use a screwdriver to pry them out! I've also used them on brake lines so they don't drip when I unscrew the hose and remove the caliper, that's a real plus. Put them on all grease fittings and it saves time cleaning them before adding grease. I would definitely buy them again.