for gearbox, you can look for EP additives

some car engine oil have JASO MA grade, can use

HDEO in motorcycles... people been using for ages

the list of additives, you also cincai tembak some brand names we also difficult to answer you
some are snake oil, some have specific function

some ppl spray water into intake manifold for decarbonize you got hear before? in some cases, water mist also can perform certain function to engine or components

majority ppl just avoid it because some do more harm than good, some are placebo

see what ajaibman says and what u think leh?

no

that reminds me of the engine bay misting system. are you referring to the same thing?

just something I saw in an old car tuner magazine.

I guess you refer to this: Water injecction wikipedia

Good info. Thank.

I guess generally, is not recommended as engine care regime.

spend on good oil, is better than spend on additive packages, which in times are discouraged by manufacturer

however, for older engines, due to fuel quality, or wear and tear, or clogging of injectors, fueling issues that may require high repair costs, it is no doubt a possible way to solve the problem. emphasis on solve, not fix.

Seafoam contains high amount of petroleum distillates and 30~50% of isopropyl alcohol, among proprietary ingredients. This product has users and naysayers. Use at own discretion to fix fueling issues - fuel filter, injector, carburetor, old fuel etc...

for other products, same cautious approach is encouraged, check for their material content, and both sides of users experiences

if a product have users complaining blown engine or causing clogged heat exchangers (some bikes uses oil coolers, not oil radiators), or other catastrophic failures, examine it more carefully.

octane boosters are products that increases fuel octane values... u need to understand fuel octane before hand, and get an idea how that specific product increases the value. simple ethanol is able to increase octane value as well.

the same fuel, with additives that raised its octane value, will burn slower. to some users, slower burning fuel means the engine feels smoother and cooler - some of the heat goes out to the exhaust

use own judgement

Regular change the spark plug will be more worthy, follow the owners manual and cut it to half.