N43 valve stem seals

[Output Flange]

Has anyone had their N43 valve stem seals changed recently? If so, who did it and how much did it cost?

I've recently acquired an E91 320i which has cost me buttons, but puffs a bit of smoke. Given everything else on it is fine, I don't mind investing a bit into it to keep it going if it's not a ridiculous figure.

Thanks!