[Lil bastard]

You don't want to use Stop-Leak !!

Leaky radiators are very uncommon for the Boxster. Much more likely toward the top of the list would be leaky hose connections (Porsche uses crappy hose clamps and a TSB calls for replacement to proper worm clamps whenever any cooling system work is done), cracked coolant reservoirs (very comon - pull the trunk floor and look for coolant pooling there, or signs that coolant once pooled there), waterpump failure (increasingly common on older Boxsters. look for signs of coolant around/under the pump), failed head gasket (pull the dipstick and look for a milky emulsion where there s/b only oil).

1st find where the coolant is leaking. Although a leaky radiator cannot be ruled out, it's not likely to be the cause. There's no savings to be found by doing the clutch when correcting a cooling system issue.