Firstly, whilst I don’t reside in WA and more’s the pity, Strata Law over there would I’m sure make the building’s raft slab, which is also the ceiling of the garage space, Common Property and therefore the responsibility of the Strata Company.
You haven’t said whether your vehicle needs to be repaired post the depositing of that lime-laden liquid, but even if it only needs to be cleaned and detailed, the best way to jog the Strata Company into action would be to lodge a Statement of Claim against them for the costs of you having that and any other remedial work on your vehicle completed, incorporating a reasonable time-frame within which you expect remedial works to their Common Property (ceiling and drainage) to be completed.
You need to get a quotation, ascertain who the Strata Managers are, and then lodge your Statement of Claim with them, and even if the “event” is not covered by the compulsory insurance (incl. liability) that the Strata Company is required to hold, their liability remains.
As you’re a tenant, it would be prudent to copy everything to your Managing (Rental) Agent for on-forwarding to the Landlord/Owner, because even though I’m not familiar with WA Tenancy Laws, I’ll bet they’re very similar to what’s in place here in NSW, where you would be entitled to claim a rent reduction due to part of the Rental Premises (the garage) being unusable.
So include a note to that effect with the copies that you provide to your Managing (Rental ) Agent, because the possibility of a rent reduction claim will no doubt encourage your Landlord, who is a Member of the Strata Company, to push things along with them.