My personal opinion on Fuel Additives, Cleaners and Conditioners is politically correct anyway, they are worth their price because thats what you pay for them and thats what you can charge other people for them if you sell the additives to them. So they are worth their price.
So are Miracle Hair Growth Additives you buy for 9.99 and those nifty X Ray vision glasses that you get for collecting 50 comics from Fleer's Bubble gum and Time Travel machines you can buy on EBAY.
I came upon this realization when I took apart my first carburetor back in 1985 and saw all those dirt and crud clogged passages that only fine piano wire or 100 psi air could clean. I could have poured 100 gallons of fuel additive through my tank and would've never cleaned those passages .00001 percent.
Only dissassembly and manual cleaning worked.So when my indy tried to sell me some the other day, I shrugged and said no.
I'm interested in everyone's opinion! Maybe there is some additive out there that can really repair cracked blocks, or worn rings or even unbend valves!
(THIS IS NOT TO BE CONFUSED with Motor Oil Quality. I swear my Life on Mobil Synthetic! )

There are some additives that have worked for me, and no it's not just a placibo effect.

Lucas Oil Stabilizer - gave me significantly smoother idle after a cold start.
Lucas Power Steering Stop Leak - stopped a steering box leak in my 87 300D
Amsoil Cetane Boost - gave me significantly quieter idle
Power Service Diesel Kleen - seemed to have an immediate quieting effect on rattling injectors
Bar's Radiator Stop Leak - stopped the heater core leak in my 240D (much easier than taking the whole dash apart)
StarTron Enzyme Diesel Additive - currently evaluating

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2004 VW Jetta TDI (manual)

Past MB's: '96 E300D, '83 240D, '82 300D, '87 300D, '87 420SEL

BG 44K is one that is worth its price....its what the dealer uses to eliminate intake valve carbon Buildup common on certain engines....every other injector cleaner was worthless in touching that.....and Saturn twin cam engines are known to build up enough to cause starting issues every 35K miles.....I ran the car to 120K when I sold it to my brother....

You get what you pay for......this is not cheap but it does exactly what it promisses within one tank full.

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Proud owner of ....
1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
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Section 609 MVAC Certified
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"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche

I'll say the same with Howe's diesel additive and Power Service cetane boost.

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1983 300-D turbo
1985 300-D turbo
1959 Harley Panhead chopper
1929 Ford coupe restored
I hang out with Boneheaddoctor at Schuman Automotive OBK#5
All liberals are mattoids but not all mattoids are liberal.

The only "problem solvers in a bottle" that really work that come to my mind is the original Bar's leak formula - (you know, the stuff that looks like rabbit chow in molasses) and Trans-X (although it won't fix worn plates, seals or bearings) The rest has pretty limited value and/or validates Barnum's theory on evolution. {flame suit on}

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'82 300SD - 361K mi - "Blue"

"Good judgement comes from experience. Experience comes from bad judgement."

listen, look, .........and duck.