TST tpms battery change?

That o-ring is very tiny and a bit hard to get on, but it does fit. I was scared I would break it, but it went on. I too have had to replace the sensor to valve stem gasket on a couple of mine, but TST sent me several spares of this gasket as well as the o-rings. Wal-Mart sells the batteries, but they are in the watch/jewelry area.

I. Did one of mine new o ring is a must and took a lot of force to push out the battery, went back easy though

Just replaced the batteries in six of mine. If you have the anti-theft caps installed you will need a very small phillips screw driver. Take out the three screws and remove the cap. Then use the install tool to hold the sensor and unscrew the cover with your fingers. The battery slides out. Install a new battery paying attention to the polarity and reassemble using a new Oring. I elected not to reinstall the anti-theft covers and just reinstalled on the valve stems. I have since requested and received some new sensor to stem seals. I need to replace a couple of them, maybe later this week.

I haven't done it but it looks like you would just remove the two screws and the plate would come off. Put the new o ring gasket in place and replace the plate. I guess you are referring to the new 507 from TST.