have you considered a fibreglass repair?

I used it to totally rebuild the plastic casing over the driving and driven clutch

the bloke before me had used it as a place to rest his left boot so it had sagged down and once it hit the revolving parts had got very hot

so as well as having a hole as big as your fist at the top it was displaced an inch downwards, so I could not simply mend the hole [without have a big bubble type fix]

so I cut off the dinner plate type cap on end and cut out about 6 inches of the distoted bit all way around

I then repositioned the cap and gradually used fibreglass kit [cloth and resin] to remake the 6 inches in between

sanded and painted you would not know it was not original