I'm reminded of the old adage: don't go broke in a limped pot. (Especially not 300BB deep.) The overbet looks like he's trying to fold out a comboish draw because he has a hand that's so strong (set, straight with 2d 4d??) he won't be able to fold it if "your flush" comes in (like some Adxd hand). But you don't actually have much of a chance to improve: paint, a diamond, a 3 or an 8 or a 9, and then you kind of can't call a shove, and you kind of can't extract value even on a blank. Somehow he's managed to run smack dab into top and bottom pair... but he has to have considered two paid holdings since you raised flop, and yet he's not afraid of that. He's not afraid of 88, but maybe he shouldn't be if you'd never limp your button with that or raise middle set on the flop.
You said he's solid so... I think, you gotta let it go. Otherwise, I humbly predict you call, river goes check-check, and he sheepishly rolls over pocket fives.