You can go whatever way you want.
If you've been wanting to do something different, this is a good time to do it.
If you are okay with the current window, I'd just remove it, clean it all up really well, fix anywhere that might cause difficulty sealing, then seal it back up and be on your way.
The only thing you really have to be careful about if you replace it with a different window is the new window has to allow for good visual access to the road and side mirror.
__________________
Steve
|