2019 SCARAB 195G, Single - 4-TEC 200 w/Catalyst, O2 Sensor Replacement Process

[fostebrian]

Engine service light appeared (no visible codes on dashboard). I took the boat to my local dealer for a diagnostic. The downstream O2 Sensor is the issue. Recommendation is to "rebuild the entire Catalyst system for $3,300 ish, or do a temporary fix of replacing the two O2 sensors for $1200. Boat has 61 total hours at the time of the code. It had the usual 50 hour service about 2 months ago. I decided I would fix it myself (two sensors with seals were about $200 from the dealer). I would simply replace the the sensors but the dealer was kind enough to take a photo of the two sensors. The downstream sensor looked very nasty, almost corroded. I figure some moisture must be getting in that area. So, since the sensors come with the seals that go on either side of the catalyst body, I thought I would just pull it off and put the new seals in....However! I am confused about the way water cools and is this ocean water or sealed/closed-loop water? The service manual requires the water supply tube be removed from the catalyst at some point in the disassembly. I did not want to dump actual coolant and end up with air in the line if this is a closed system. Unfortunately, I am unable to determine what is what concerning the type of water being supplied. I am not a SCARAB mechanic but I have replaced the entire catalytic converter and O2 sensors on a RAV4, lol. So, I do not fear the engine but I would like some advice to remedy what I perceive is the need to seal up that catalyst a bit better after installing the new sensors. I am not made of money to carelessly toss money at repairs. I take care of my things and $200 sure is better than the alternative. But, I would appreciate any advice if anyone has noticed the O2 Sensor Bulletin for 2018 or has had a similar issue and replaced the O2 sensors and seals that the part comes with. Thank you.