I gave up trying to remove clamps from top, took the aluminium plate off the bottom and a mere 5 hours later the tank was out (many tea breaks)
discovered the oil filler hose (one with flexi bit) was split so just waiting for a new one to arrive on Monday then can put it all back together, not sure if I should replace spring clamps with jubilee ones at same time, bought original but used tank, looks mint compared to one taken out but not sure I should trust it to last too long. Lastly I found a Porsche specialist only a mile from where I live so can pick up 50/50 mixed Porsche antifreeze for £6.50 a litre,
Total job cost £135 - Used tank £45, New oil filler tube £36, Coolant £13, for a full set of spring clamp pliers £40
Boxster S
Threaded Mode
