Toyota had sludge issues on both the I4 and the V6 engines in all the 4th generation Camrys; that's 1997-2001. If believe Toyota extended the warranty on these engines to cover sludge issues to 8 years or 150,000 miles, whichever occurred first. Your 98 is well beyond the 8 years.
As far as your particular engine is concerned, if you think you have a sludge issue a mechanic can tell easily by removing one of your valve cover gaskets and visually inspecting the engine there. He will opt for the front one on your V6; it's a lot easier than the rear one.
As far as your turn signal problem, it does sound like it's in the switch inside the steering wheel, as somick mentioned above.
Mike