It is actually easier on the 90 series than the Surf. Once the panels are dropped from under the car, you need a very long extension to undo the 3 bolts from the rear and the starter comes out the wheel arch.
They seem to give a little warning before they go.
From experience on my two Toyotas you get a few miss engaged turns of the key as a warning sign... plus a couple of get out of jail starts where the solenoid rotates and makes contact on a less burnt part of the contact ring inside, but it does go downhill pretty quick.
The Toyota Mechanic I spoke to when working out if it was the same as the Hilux said it is low voltage that causes the burn on the contacts so keep the batteries in good nic!