There are a few different types of synchro rings out there for the 3S trans. The early 1G units had 3-5 gear synchro rings that had an organic lining. This lining is sensitive to fluid weight and type and can fall apart even if the vehicle is kept in good condition. We upgrade these to the lasest version of synchro rings from Getrag (the trans manufacturer) which is a steel ring with a bronze lining. These not only shift better but last a lot longer too! They are also not sensitive to the oil.
Here is a picture of old style synchro on left, new on right:
There has also been a problem with copies of the synchros duplicated in China for these units. The Chinese synchro rings are terrible. They don’t work and grind immediately. In the pic below a Chinese synchro is to the left, OEM original Getrag on the right. It’s easy to tell which are the rings from China as they are all brass, but the OEM Getrag rings are steel with a bronze inner lining: