I've used "mechanic in a bottle" on my f150 v6 4.2 ( 168,000 miles ) because I needed it to run without leaks a few months more. Sort of works.
If you go to your local garage and say " I'm not going to do a proper repair or use your shop, but I'll give you 100$ for your honest opinion ".
They will say, "go ahead, swell everything up, it might work for a bit. But, it will be 10 x's worse when the elixir breaks stuff down"
If it's on its last leg, go for it, if you are holding off on a repair, expect far more stuff to replace because of it.