Ive had success restoring a rusty sender unit of another bike by
spraying it with oven cleaner leaving it stand for 3 or 4 mins and submersing it in
water for another 5min the water will dillute the oven cleaner and should not eat away
the part(but keep an eye on it). then submerge/rinse it thoroughly in clean water
dry it with air and leave it in the hot sun or on a warm heater to get it total dry.
no guarantee.but it has worked for me before.
On closer inspection of your picture,
it does look beyond saving.
sorry im a bit blind mate.
I will more than likely have one Phil but can’t check until I get back to the UK.
If you find one first just let me know
I’ve sent you a pm Phil