Welcome to Defender Canada! 
Airmar DST800 Non-Valve Housing O-Ring Kit - 20-519-01
$9.79
Airmar DST800 Non-Valve Housing O-Ring Kit - 20-519-01 Item # 1077588
Description
O-ring used to replace yellow o-ring when retrofitting a DT800V and DST800V in a housing without a valve. This black o-ring is designed to form a watertight seal.