Re the sen-813 SENSOR I had this leak, new O ring it IS a specific size and cheap enough from Guzzi Dealer BUT the sensor IS very expensive from Guzzi I found a car parts dealer with the replacement part for £25.95 as opposed to the £130+ Guzzi wanted the same part fits a whole load of Guzzis as well as MV Brutale and some Ducati bikes I have posted all the details on the site www.guzziriders.org hope this helps