Yes, valve guides and seals are a common concern on that engine. You only need them when the engine starts excessively consuming oil, not based solely on mileage. But by 200k miles, a lot of engines usually have it done. Monitor your oil consumption and see what it turns out to be, this will tell you when you need a valve job.

If the transmission is not slipping or flaring, I seriously doubt that it is a transmission problem. Is the engine hesitating? Transmission life depends on many factors. Some barely make it to 150k and some go over 300k.

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Ali Al-Chalabi

2001 CLK55
1999 Dodge Ram 2500 Cummins Diesel
2002 Harley-Davidson Fatboy
Merlin Extralight w/ Campy Record