I have a pair of 8-speed Ultegra shifters that hadn't been used in 10-years. They were extremely gunked up. Neither shifter worked. The hoods were also de-vulcanized and very sticky.

I took the shifters off the bars, took the hoods off, sprayed a liberal amount of WD-40 into each shifter and let them sit for an hour. Then I threaded a shift cable into each one and put my foot on the other end of the cable to put tension on it. I then shifted up and down on each shifter probably 30 times. They were both working well at this point so I sprayed more WD-40 in each and let them sit overnight. The next day they were working perfectly and still are a year and a few thousand miles later.

As for the hoods, I made a roughly 1 part simple green to 5 parts hot water solution and let the hoods sit in it for a few hours. I had to weigh them down so they were completely submerged. Then I scrubbed them with a wet towel and let them dry for a few hours. This got the sticky rubber layer off them.