Mechanic in a can, has it ever worked for you ?
 

Ive been working on my 2003 Honda Accord ( rental house tactical assault vehicle ) I have a sticking valve in the trans. The filter blew apart, and dirt, and pieces of the filter are littered throughout the transmission .
I have drained and filled it twice now, and removed and cleaned out all the solenoids . I got it working about 95% of the time, but it will still occasionally stick, and not shift into 3rd . ( I dont really care, Ill drive it like this anyhow) .
I just found a bottle of Lucas transmission treatment in the trunk of the car. I dumped it in thinking what the heck, nothing to lose . I'm probably going to have to make real repairs at some point anyhow, but either way, I am just going to keep on with the drain and fill till I see no more particulate in the fluid.
I'm thinking of all products like this , tire slime , bars leaks, oil and power steering stop leak, head gasket leak stopper , ac leak stopper, and enhancer , there are tons of them on the market. I cannot recall ever seeing one really work .
I did have one customer with a blown head gasket on a 360 in a dodge truck, and to my surprise, that metallic paste they dumped in the radiator did work . For about a month. Then we had to replace the heater core, and radiator in addition to the head gasket repair
I have always believed it all to be snake oil . Has it ever worked for any of you ?

I had a coolant leak coming from the engine block in an old Honda. I did not have the time or money to repair and it was a small leak anyway.

I poured in a bottle of Bar’s Leak stop and it fixed it. I don’t think I’d do that to a car I loved and cared about, though.

Tire slime works on my off-road tires. I have it in one of my mower tires and in the right front of my tractor, and one of the golf cart tires.

I've had power steering stop leak work on minor leaks. Cant think of anything else.

Many times I have found myself with an unexpected problem, and managed to get through it using a magical product that can be applied in many situations: Bourbon.

That is mechanic in a bottle :)

Bar’s Leak stop [walnut shells ground up]
was used by caddy in the first run of the northstar v8s from the factory
as they had problems with the alloy heads fitting the alloy block

Back when I used to ride motorcycles I used a tire slime type stop leak when I found my rear tire low just before a Sunday ride up to the Rock Store. Put it in, pumped it up (tubeless tires, gotta love 'em) and declared it OK to ride. My wife was a little leary but went anyways. We had a good day.
Another time when my '85 BMW 325e exhibited the generic weak head casting that allowed coolant into the oil, I used Bar's Stop Leak. Put it in according to the directions and it worked. Kept it in there until my brother found a replacement engine out of a 528e.

Steering rack
 

About a year and half ago I told my indie mechanic to replace the steering rack in my ‘02 Accord. I just wanted it to run well a while longer. He said “it’s not that I want to turn away work, but you might just want me to put in some Lucas power steering treatment to buy you that bit of time.” Well it’s worked so far and the car keeps going. I did have to top up the fluid once, but that’s it.

Lucas stopped the PS drip in a car for me. Was very thick and it took a while to warm up when cold but it was still working 3 years later when I sold the car. Better than replacing the rack, to me.
Black pepper stopped a heater core leak for me when I was 100 miles from home. That stayed good a couple years until I replaced the core as a preemptive measure. Not real proud of that one but desperate men do desperate things.:D:D

I tried Fix-a-Flat recently. Slowed the leak, but no cure. 'Course, it was a crack in the wheel shell that was the culprit, so I wasn't totally surprised.

My 95 Grand Cherokee had a bad head gasket that I fixed with a bottle of something. Followed directions to the letter and drove the truck for another 2 years perfectly fine before selling it.

Damn, that's the one thing I didn't try on my 3.2 valve guides.