My 996 was losing 1-2 cups of coolant per month - not a lot but enough to be noticable. Six months after replacing the cap with the lastest 04 version I still haven't had to add a drop.
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1999 996 C2 - sold - bought back - sold for more
1997 Spec Boxster BSR #254
1979 911 SC
POC Licensed DE/TT Instructor