I was personally thinking of using my favorite rural torch...
Put a rolled up towel in the bell, smoke a pipe or cigar, take several long puffs and hold, finger low Bb, stand in front of mirror, blow smoke through mouthpiece - you'll see the leak(s)... :mrgreen:
If you want a light show, do it in a dim room and get a friend to wave the rural torch around the sax, it'll pick up the smoke trail from the leak.
Kind Regards from rural Weymouth (those city folk don't understand, don't get many sax techs in rural area's, or much else for that matter, we have to do it all ourselves, or it doesn't get done...

)