I know how you feel! The off-leash dog park is the only place Hugo can legally be off-leash, so it's hard to not take them. Plus it's his favorite place in the world. I worked on Hugo's recall for a long time and didn't see any progress until I put the long line on him and made it stay on. If the long line was off, I NEVER called him in. I only called when I could real him in if he made the decision to ignore the call.
When you go out to the park, does he ever check in with you? Look toward you to make sure you're there, come back to check in, etc? I REALLY wanted Hugo reliable at the dog park, so I took him there every singe day for at LEAST an hour, more like 3 on the weekends. I kept him on a long line and I drilled recall like you wouldn't believe. I rewarded him with nasty smelly canned dog food and bison tripe every time he even looked at me. I also played with him a LOT. We played modified chase (obviously he runs much faster than me so he would just zoom really close to me and I would fling myself at him like I was going to tag him and he would zoom back around). We also played a ton of tug with toys he valued. I let him play with other dogs but ONLY when I said "go ahead." If another dog approached him (can't control other people's dogs) I would give the "go ahead" cue, as if it was my intention all along.
He made HUGE leaps in that time period, and it was right as he was the age your guy is, in which our boys are bratty teens. : ) He comes on the 1st call now, hasn't blown me off in months and is very nearly 100% on not leaving to greet another dog with out my permission. Occasionally if one passes close by he starts to head off to them (esp. if he knows them) and I have to recall him and then give the go ahead if it's a dog I know he can play with.
I know it's easier said than done, but I would really avoid letting him self-reinforce.
I know that's a little be of unsolicited advice, lol, but as for recallers, I plan on taking it. I know it's expensive, but I do really well online classes and am really good at following a well put out schedule.