Geezmeister is the master advocate of multi reX.
If it's still leaving some sludge on the glass after one reX, then reX it one more time.
Bee sure to rinse it well with cold, dry acetone when complete as there is lots of unseen garbage in that mother liquor/acetone that it's been sitting in. A layer of that garbage will coat the crystals if they are not well washed after the reX.