I had a 97 Diamante bought from Texas that had 150K miles. It ran great and I sold it when it had 240K miles.
Then I bought the 2002 Diamante. I love the way they look, the one I got looked brand new. After one I got the following issues.
1- Heater core went bad, started leaking inside the passenger side. Cost me 1000$ to get it fixed.
2- Trans started jerking going from 3rd to 4th gear.
This car was a nightmare. Thank god I sold it after 8 months, lost $3000.
Bad car. Don't ever buy Mitsubishi unless it had a very low mileage.
It's called a transmission flush. Try it. And wow, 2 repairs after 100,000 miles makes it a terrible car? Not every car is problem-free especially after 100,000 miles.