Good call on getting the leak fixed... MAF cars definitely hate leaks. I have a few couplers to pressure test piping and then spray on some soapy water, but even then it can be a challenge depending on where the leak is.
The HKS BOV design is still one of the best in my opinion since added pressure really helps the piston seat and isn't nearly as finicky as some other 'quick-acting' types. The main challenge is getting one that isn't an ebay clone. Given the inherent design, the clones can still do fairly well... but I've seen the center smaller valve for lighter throttle releases not function, and also seen them still manage to leak with questionable seating/and springs on the back end. You can work around it a bit, but if you can find a new/used authentic, you'll save yourself a lot of headache. Used clones vs. used authentic don't seem to differ too much in price $80-$150 just because most guys think theirs is authentic. New authentic are in the 400-450 range.
IS300 - 2JZ-GTE, DIY custom sequential 31psi at 2800rpms, yeehaw.