It’s a long shot, but if you were in Patagonia there could even be a Welsh influence there due to the colony of y Wladfa. In Welsh the double L is pronounced like…well, we don’t have an equivalent sound in English, but it’s basically put your tongue up against your front teeth and blow. I could see that resulting in the “zh” pronunciation you heard.
Yeah, that line is downright subtle compared to some of the rest of the lyrics, which make it perfectly clear that Jack and Diane are constantly banging.
Jack he says "Hey, Diane, let’s run off behind a shady tree Dribble off those Bobby Brooks Let me do what I please"
Speaking of song lyrics that need a minor change, “Dribble off those Bobby Brooks”?!? I always thought it was “Jiggle off”. Maybe it’s a lyric mistranscription, but I checked a few lyrics sites and they all say “dribble”.
That sounds completely jarring in my dialect of US English. If you aren’t/won’t be good, I will spank you and If you don’t behave, I will spank you! but not *if you don’t be good, I will spank you! As an imperative, it’s fine, though: Don’t be good!.