When I rebuilt my DISAs I always wrapped some premium Teflon tape around the seal to make it snug. I used a brand called fastape or fasttape; it's three times as thick as typical Teflon but more importantly it's color changing: turns dark under pressure so you can do a test fit and confirm complete seal.

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2011 E70 • N55 (me)
2012 E70 • N63 (wife)