Search is your friend. Search on "300E lifter". You will find lots of threads. Genarally lifters are not "too hard" to replace but it depends on your skill level. But everyone seems to agree that is the trouble and not really a huge deal unless it goes unfixed for a while and causes cam damage as Steve said. Steve's 3rd post is what you need to know. He is usually right even though I don't understand what he says half the time.

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1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra