Mine was split where the overflow hose is , someone cranked the cap down so hard it hit the spigot and cracked it , so no pressurising ......any how .....doesn't make any issues (still overheats properly in start stop traffic ) so as long as it's not leaking on the paintwork I wouldn't loose any sleep.

I took my leaking tank to a specialist plastic welder in Ballarat, Victoria, Australia. He rewelded the entire seam and charged me $40au. It has been better than new ever since. Seems to me to be the cheapest and easiest repair, just remember to get the entire seam done.