I've invested thousands into Stucchis VEP 17 HD couplers. After I still experienced failures I was told by my supplier (a local hydraulic repair shop) that I needed to get the VEP HDL couplers if using them for high impulse/vibration applications (this seemed like an avoidance technique as they are the ones who recommended, and sold me, the original couplers knowing what my application would be). High vibration applications would be things like breakers, ho-pacs, etc., which we do use. (I honestly struggle to come up with very many "low vibration" hydraulic attachments). Regardless, I spent the money to upgrade both machines and attachments. This adds up when you have (6) pairs of 1" couplers to buy (they are just under $400 per pair). The "L" in the part number indicates that it will have a locking pin, and subsequent holes, to prevent the coupler threads from coming loose due to vibration. In my applications this does sometimes happen (usually with the ho-pac, and hammer, but not so far with my crusher bucket) and when it does the seals in the couplers go bad (maybe they get cut?). Once this happens they tend to constantly leak. In theory the locking pin seems like a pretty good idea. In actual use they do not perform as promised. Despite the locking pin the coupler will still come loose enough to leak and destroy the seals. They won't come all the way off (never had any of the non "L" style come off either because the operator will notice that the attachment performance suffers from restricted oil flow caused by coupler coming loose) but they will still get damaged. I plan to contact Stucchi, maybe even return some to see if they will warranty them but I don't hold out much hope for that. Right now I have removed them and am just screwing together the JIC fittings. It's a bit messy but only when actually connecting/disconnecting the lines...not during operation of the machine/attachment. This also has the added benefit of not having to wonder if the coupler is causing any performance loss, and/or extra heat, due to possible restriction of oil flow that is inherent in hydraulic quick couplers.