Open out the agreement details then only we can read and debate. Now it's only heresay.

1) Why wasn't Malaysia insist of review the new rate in 1987?
2) Does the agreement has a clause that both countries will have reserved the right to review the price in the future when it deem to be unfair to either one of them?

And a lot of question marks. But agreement/contract is signed and must honored regardless. Like how Malaysia cancelled some project with China and need to compensate for the cancellation of the contract. That will apply the water deal as well.