About six months ago I had two coils (#1 and 2) fail on my 2000 ES300 w/ 75k. A month later one of those coils failed and had to be replaced again, and now I just had a seperate coil fail (#4) this past weekend. Is it common to have the coils all start to fail at around this age of the car, or is there something underlying causing these failures? If this is common, should I bite the bullet and replace the remaining three coils now to avoid the hassle later? I'll probably be driving this car for the next 3-5 years still.