I am thinking of changing to synthetic oil because my 99 disco II has 121,000K. Does the system need to be flushed or can I drain the regular oil and just fill it up with syntec?

 

I was taught in school that changing to synthetic that late (in terms of mileage) is not a good thing. Damn if I remember why, but others may think different.

 

Flush the engine first and go for it. Be prepared to possibly change it early after switching over cause a synthetic will loosen up alot of old junk. Also keep an eye open for any new oil leaks, sometimes an old leak will get worse on synthetic.
As for the logic, I would do it.
Mike

 

How do I flush it? I may just need to let a shop do it the first time and I'll continue from there

 

You can get Mobil One Highmileage synthetic now in 10w30 and 10w40. I changed from
the reg Mobil One to the highmileage and it almost stopped all the little oil seepage
spots on the motor.

To flush the motor you can use ATF six qts and a new oil filter and let it idle for 20 mins,
not driven and then change it as normal, new oil and oil filter.

 

Good idea.
I doubt you will find a shop that can flush your engine, For under $15 you can do it your self.
Mike

 

Yeah watch for leaks/seapage after. I switched an engine over once and the front main started seaping right after.