Nothing wrong with 20,000 kms on GBox oil, but a change might make it feel better nonetheless. Just changed mine the other day. Was 35-40,000 old and still clean. GBox feels mostly the same.

If the mounts are cracked you can fill them instead of replacing. A few people are against it but two of my mates did it with their EF8's (one with Sikaflex, one with polyurethane) and they both feel totally fine to drive.