You can prevent this yellowing from happening by storing the console away in an airtight, dark container (such as it's box) when not in use. The console has been fully cleaned internally, all buttons are as responsive as you would expect.
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1pcs For Gameboy Classic GB DMG GBO Battery Cover case Replacement For Game Boy console battery door back Battery Lid Door Shell
Aliexpress UK
Supported Formats: Multiple classic console emulators. ✅Plug & Play Ready – No setup needed — simply power on and start playing. Battery Life: Up to 6 hours of continuous play. We stand by our products.
eBay
New 2000mAh 3.7V Host Battery Rechargeable Lithium Battery or Nintendo NEW 3DSLL 3DSXL N3DS 2DS GBA SP Gameboy Game Console Cell
Aliexpress UK
Original Gameboy PCB installed in a New shell with an IPS screen. PCB is used hence the Used status in the description. Packaged with enough extras to get you playing straight away. Free gift - 4 x AA - Game - Stickers
eBay
10pcs/lot Black and grey For Game Boy gameboy GB gb Console plastic Lens Screen Replacement Repair Part
Aliexpress UK
Nintendo Gameboy Colour Clear Shell Stunning Amoled Screen Mod Installed Game not included Battery’s not included
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2PCS For LCD Screen Protector Protective Film for Gameboy Color for GBA GBA SP GBC GB GBP GBM for Gameboy Advance Game Console
Aliexpress UK
Made in Japan, this handheld system has a resolution of 160x144, perfect for on-the-go gaming. ———-This example is in beautiful condition and works perfectly. No batteries or box included.
eBay
1PC Transparent Acrylic Magnetic Cover Case For GBM Game Console Storage Box For Game Boy Micro Game Console Accessories
Aliexpress UK
You will receive one in similar condition to the one in the photos with one of the serial numbers listed above. The back of the unit is in good condition with little to no noticeable wear. The buttons have been cleaned and are in good condition.
eBay
1PC Transparent Acrylic Magnetic Cover Case For GBA SP Game Console Storage Box For Game Boy SP Game Console Accessories
Aliexpress UK
Gameboy Advance SP - New shell - IPS screen - New battery - Charge cable Free gift - Game - Stickers Listed as used as the PCB is original.
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for Gameboy Game Boy GB Game Console Accessories Kits Replacement Housing Case Cover Shell
Aliexpress UK
This involved applying a hydrogen peroxide solution and exposing the shell to UV light to remove yellowing and discoloration. Each component was thoroughly cleaned. Retro Brightened Shell.
eBay
JCD 1Set Colorful Rubber Conductive Buttons A-B D-pad For Game Boy GBA Game Console Silicone Conductive Start Select Keypad
Aliexpress UK