Our IXL Tastic is still going after 10 years of daily use. The heat isn't super powerful but we have ducted heating so its neither here nor there. The fan however is quite good. Not saying the Tastic is the best but its still going with the original lamps......and it was cheap to buy and install.

We have a similar bathroom, walk in robe set up. Exhaust fan is in shower recess. In Perth also. No problems with moisture build up. If you have fan only in wardrobe, you are letting the steam get to wardrobe. If the fan is in the shower recess, then most of steam is extracted immediately.

contact an electrician and they should be able to find a suitable replacement and also advise about how to cover any gap

are you after a exhaust fan only or a exhaust,light and heat? you basically need to look at the m3 / hour, 555/M3 is at high end and below 255/m3 is at the low end. You don't need to spend a lot of money to get a good exhaust fan they are quite but if you want no noise try an online fan this will be away from the fan opening. There is a lot of option so pick one you like the look of but make sure the m3/hour is good and position of the exhaust helps a lot try and have it over the shower area this will help with steam escape quicker.