crush washers are fine as long as you use a new one each time and remember that the final drive (Diff) drain plug is sacrificial (so you don't strip the thread in the Alloy diff housing) as in that they will snap if you exceed the torque spec of 15 pounds if memory serves me right.
A while back I can't remember who it was but it was a very talented English guy that made beaut diff drain plugs which were made with an O Ring groove and used a Hex Key to do up, it still has a magnet like the original and I love mine.
If you do a search you might find the thread he started and he may be willing to make more
I use slight smear (only) Selleys 401(temp silicon) on all my drain bolts washers and only just tighten them up firm never had one leak or come out yet, have reused them several times as I am not compressing them and use Alloy washers not crush washers