Rain repellant or no rain repellant...........irrelevant really
The purpose of rain repellent is give the crew a clearer vision through the windscreen in heavy rain. On countless occasions when approaching to land at Pacific atolls and the visibility is momentarily lost due to a very heavy shower , a quick squirt of rainbow rain repellent immediately caused the rain covering the windows to break up into individual blobs or droplets and it was quite amazing you could see between the blobs and certainly enough to continue visually quite easily. We swore by the stuff.
Later windscreens were coated by a special material which in theory gave better visibility in rain. Experience showed that that coating soon wore away and it became useless.
If inadvertently the rain repellent was squirted on a dry or merely damp windscreen it would form a white residue on the windcreen. The only way to clean it off was with a special very expensive bottle supplied by Boeing I think. An easier way and far less expensive, was to shake a bottle of Coca-Cola then squirt the contents on the windows. That stuff cut right through the residue, quick smart. That is probably why, as many teen-agers later discovered, Coca Cola could eventually rot their guts!
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Some 737 pilots in SE Asia would sometimes carry in their navigation bag, bottles of commercially available Rainex car window rain repellent, which was quite effective. At $5 a bottle, it was good insurance. Of course it had to wiped on to the windscreen before engine start if the forecast indicated heavy rain at the destination.
In the case of the Bali accident, if rain repellent was installed, then its immediate actuation on entering the area of heavy rain nearing the MDA could have allowed the crew to keep the runway in sight at that critical period rather than letting the aircraft descend in the blind hope of spotting the runway through the rain when there was no hope.