I have issues with my FF connectors under pressure too. In fact, I wrecked the seal on the female side trying to hook up my grapple after extracting it from the snow last week - now I'm not finding anywhere who advertises that o-ring for the 16028 couplers so I might have to go to a specialty shop and hope to get lucky. It oozes oil, so this is not a delayable repair.
I've been meaning to make a tool to connect the couplers with a square threaded clamp, because I'm tired of using my ad-hoc ratchet strap work-around. I relieve the pressure from the tractor side religiously whenever connecting or disconnecting (which is a PITA in of itself), but thermal conditions seem to always rear up on the implement end and make things annoying.
That said, I wouldn't want to go to the Ag style on my FEL. There's just way too much crap that ends up all over those fittings when I'm using a bucket or pushing through the brush without an attachment present (like mowing).