use the service manual and red eye kit. free download here,
http://www.valkyrienorway.com/download.html All of so called rubber is Buna-N which is designed for 10% ethanol. 15% eth will harm it over yrs of service how many yrs don't know but it could be calculated.
always use a stabilizer every tank. I prefer the new stabil which emits fumes which coat parts of the tank and carbs not immersed in fuel.
I also use TC-W3 fuel additive. keeps carbs clean, lubricates needles moving up/down inside of needle well, and keeps head valves clean. Also will see 1-2 mpg increase.
can read here
http://www.ls1.com/forums/f48/been-testing-oil-91206/If u decide to take them apart, when removing the carb bank, remove both upper engine supports per the manual and the carbs will slide right out. no need or reason to remove radiator shield and the headaches it will give you. the you-tube guy didn't read the manual.