A grommet failing to cause all of those? I doubt it very much. When has this started? Battery is a good starting point (it really should be the full size one and if it's still original, it's probably on its last legs). Charge it if you can, preferably overnight.
Battery should really be one that's 74Ah (yes, that's massive, and yes, it's expensive) and don't shut the boot when you change it. 10mm nuts. Remove the negative side first, then the positive and go the other way around when reconnecting.
Volume control issues: it's a "known problem" for some radios, though it generally occurs when it's cold. I'm assuming it's still an original radio at this point; If not, there's probably a wiring bodge at fault and it's going to require a complete troubleshoot.
- Bret