An interesting question: Are military equipment sold with guarantee? If an equipment fails within guarantee period, does the vendor pay or compensate something?
If this was a FMS (Foreign Military Sale) it is not unusual to NOT have a warranty - the manufacturer is selling to the US DoD not to the end recipient, the DoD isn't in the warranty business. You can pay extra to get a warranty. If it was a DCS (Direct Commercial Sale) then its whatever the contract says. IIRC Singaporean sales are usually a combination of FMS and DCS, frequently the main hardware/platform is DCS, the weapons FMS.