My apologies ahead of time for the length of this post. So allow me to tell you about my experience in replacing the rear glass. I have a 2019 AWD (manufacture date 5/4) that was delivered to me in flawless condition. The car originally came with a dark grey tinted front and rear pano glass. A week after taking a delivery the local tint shop damaged my rear one by overexposing it to a heat gun (hairline crack). They also put a dent in my car with the same before mentioned heat gun. Some days later, the tint shop paid for my local service center to fix the dent and replace the glass, but they were not able to symmetrically align it as was done with the factory installed original. Therefore, they had to replace it once again. The 2nd time around the rear glass was sitting 2-3mm higher then the front glass causing wind noise. In addition, both failed attempts utilized a supplier providing the bronze hued glass that turns orange when wet. Pretty cool but when it doesn't match the front glass and the rest of your tint it looks odd.
Well going forward having lost all faith with my local service center here in Southeast Florida, I decided to try another one an hour south of me in Fort Lauderdale. They agreed that the glass needed to be changed for a 3rd time, but when I picked up my car I noticed it was misaligned once again on the lower edges. The shop foreman stated that a 2-4mm variance was within company guidelines, so they would not make another attempt. In other words, Tesla basically acknowledges they have a fit and finish issue at the factory and service levels.
At this point, I basically had given up on getting my car back to its original state. Then however a few weeks later I noticed a large scratch within the 3rd brake light compartment and missing sections of interior defroster lines. They basically used a less then quality piece of glass. Therefore, they were obligated under warranty to make a 4th attempt. I am happy to say that the glass is not only aligned properly with all defroster lines intact, but I was lucky enough to finally have the original tint that matches the front driver's portion.
Anyhow, I have several learns from this experience. If they replace your glass there is a good chance it could be misaligned. In fact, I've inspected brand new factory builds that come with misaligned glass but fall within the allowed variance. Tesla also sources glass from multiple suppliers so there is a chance that your front and back could be mismatched. New builds I've looked at currently appear to come with front and back glass that turns orange (bronze hue when dry) when exposed to water. I was told all replacement glass right now is the same, and regardless of the supplier utilize the same exact part number. This means there's no effort made for an exact match. Having said that, my 4th and hopefully final replacement came with the original grey tint. As far as the damaged defroster lines go, this is due to a poor manufacturing process or the way they are shipped and prepped at the service center. The shop foreman showed me how rear glass is packed in fives with tons of tape and foam. If they are not careful undoing the tape it'll tear the defroster lines off. Ultimately, my advice to you it to allow them to repair the defroster lines if they offer it as an option, or purchase a repair kit online and do it yourself.
