My original tank was 10 years old before it cracked round the top and leaked ( old style with small cap ) , I now have the new one with improved cap ( genuine landrover parts about £35 )
I would just drain old tank & fit new tank & cap then refill tank with neat antifreeze ( as you have diluted with water top-ups ) , Then see how it goes if level is ok after a while then you can drain/flush/bleed the system if you like ? maybe in warmer weather ?
I would just drain old tank & fit new tank & cap then refill tank with neat antifreeze ( as you have diluted with water top-ups ) , Then see how it goes if level is ok after a while then you can drain/flush/bleed the system if you like ? maybe in warmer weather ?