If your fix is too strong, and you fix too long, then washing has to be extended in order to wash out the fixer and byproducts.
Seven year old fixer that has had particles floating in it and has been heated to 100 F may very well be shot.
The "leader test" just means dropping a drop of fixer on an undeveloped film and leaving it there for 30 seconds. Then immerse the scrap of film in the fixer and time how long it takes before you can no longer tell where the drop was (i.e. the film is no longer milky and is fully cleared). If that time is reasonable (around one minute?), your total fixing time should be twice that for traditional films, and up to three times that for T-grain films.