crystals don't have notches...
I thought you might have given us a decent pic by now, or at least told us what accelerator it is!
The GVP A3001 has pin in the left lower position as shown (poorly) in the provided picture, so 1) orientation is correct, 2) with the legs too long (as seen in pic) it will fall out again, 3) while a 16MHz crystal "should" work, a new, known functioning replacement crystal would be best; while I have used DigiKey for the past 25 years for buying crystals and the like, it is 6 am and I'm on my 7" tablet and don't feel like getting up and doing a search, but they have a very complete catalog of these.
Once working, seal it in place with a drop of hot-glue; my gun and supplies came from WalMart for <$10 USD
