re:
I have used 44K to decent success (it was on a new-ish car) and I have heard great things about Seafoam, there's a can of it in my 4Runner right now.
One thing I thought I should mention - I worked at an independent BMW/Saab repair shop the last three summers, and one day this German salesman came through the door trying to sell some flush treatment. Long story short, the stuff is absolutely amazing.
It is extremely potent. Much more so than 44K. We did a before/after compression test of the parts manager's E30 BMW 325is, and after running the oil flush through, compression went up an average of 5 psi per cylinder. Not bad. And the car ran noticably better at idle after that.
The stuff is called TEC 2000. Spelled just like that. But unfortunately, it is extremely hard to come by. I have never seen it anywhere online or at any of the run of the mill auto parts stores. The stuff had German and English writing all over it, I believe it is imported from Germany.
They have an oil flush and a fuel injector cleaner. The injector cleaner can be used just like seafoam. The oil flush goes in the oil filler and you run the engine for 10 minutes. Then, drain the old oil and refill with new oil.
As an example with my car -- I had nice golden looking oil before I did the change. I ran the stuff through for 10 minutes. When I drained the oil, it came out BLACK.
It is GOOD GOOD stuff. If anyone is in the Virginia area I can tell you where to pick some up. Unfortunately other than that, I have never found the stuff.
Cheers,
Patrick