Well, sine nobody seems to want to reply...
...to your question, jsmith, so I'll jump in:
For the most part a "flush" in a can may or may not work.
Lubeguard is highly regarded by some. The "power flush" at the shops where they pump solvent through your oil system is not very well regarded by many as it can destroy your gaskets and seals.
My personal recommendation is to try a product called Auto-rx which you can find @ auto-rx.com. It is a cleaner vs. being an oil additive. I've used it on my SVX, I just put a treatment into my F250 and changed out the oil & filter from the 1st 750 mile application in my 420SEL yesterday.
It does not alter the chemistry of your oil, cleans gently over a 500-750 mile period, and can help you if you have seal leaks.
I believe it works as is described and it won't hurt your engine. I have been very impressed with the results I've seen and this is not a "snake-oil" product, IMHO!
'91 420 SEL @ 199K, '92 SVX @ 181K, '93 SC400 @ 86K, '93 Kaw ZX-11 @ 30K, '87 F250 @ 181K , 2001 Valkyrie Interstate @ 6K, Y2K Honda NightHawk 250 with 1.5K, '88 420SEL I.@ 179K & the 2nd latest, an '88 420SEL II.@ 210K runnin' parts car, '85 F150 300/NP435