You don’t need to replace it yet — most of these stains can be lifted unless they’re etched into the plastic. Based on what you described (yellow/brown underside on plastic/melamine), here’s a realistic, step-by-step “try this before replacing” plan:

 Step 1 — Start Simple (often surprisingly effective)

• Hot water + dish soap
• Non-scratch sponge

Scrub firmly for a few minutes.
 This removes surface urine/mineral buildup first before stronger methods

 Step 2 — Baking Soda + Vinegar (best first “deep clean”)

• Sprinkle baking soda
• Spray/pour white vinegar
• Let it fizz and sit 10–15 min
• Scrub + rinse

 This combo breaks down uric acid + mineral stains

 Step 3 — Hydrogen Peroxide Paste (the “miracle” stage)

If stains remain:

• Mix:
  • baking soda + hydrogen peroxide → thick paste
• Apply generously
• Leave 20–30 minutes
• Scrub + rinse

 This is the closest thing to a “bleaching without damage” solution for plastic