I have a Constellation C shape case, its crystal was replaced with a non original generic one.
I am wondering if the original plexi hesalite crystal of this Constellation 168.029, can still be ordered.

Apart from the omega logo in the centre , are there any drawbacks to the generic crystals?

 

Sone generic crystals are acceptable for some cases, however, the OEM crystals with the correct tension ring are always preferred. You didn't say what colour your case is so the Omega Part Numbers for your crystal are:

PZ5118 - With Steel tension ring
PX5118 - With Gold tension ring

You can get your watchmaker with an Omega Parts Account to source and fit one for you, or you can DIY.

Example:

https://www.ebay.com/itm/Omega-Plex...2071?_trksid=p2349526.m4383.l4275.c2#viTabs_0Purchases made through these links may earn this site a commission from the eBay Partner Network

 

Mine is in steel with the white gold bezel, guess I need the PZ5118, is this crystal hard to find?

Is the tension ring directly behind the crystal, thus it’s visible?
Is the gold tension ring version made for the 14k gold case constellation models?