Someone I know purchased a house and is in the process of cleaning. A tough spot he got into was in the master bathroom his shower has the older sliding door type. It is in good condition, it still shines, but in the track and by where the track and shower floor meets in nasty 25 year old grim and stains he believes. What is a real good powerful cleaner to use to get rid of all that nasty stuff? I thought simple green but sure there's way stronger cleaners out there.

Might need one of those steam cleaners.  Soap scum is pretty tough stuff.

For minerals and soap you might try CLR, it works fairly well. If it's mineral on tile you could try acid but be careful of acids on metal surfaces.

I will try and have him get me a picture so I can post to show you guys what I'm talking about.

Simple green kicks ass on soap scum and any "grime" (icky stuff containing grease).

 

If it has scale, you may need a residential HCl lime removal product and 15 minutes to half hour of repeated applying and removing, with a light scrub prior to removing. Not a lot of elbow grease, just attention. And gloves, fresh water decon source, eye protection is mandatory, and ventilation.

 

CLR, Super Iron Out, etc. will not remove highly structured scale that has accumulated over a long period of time on some surfaces, and depending on the relative constituents of the hardness. Not all scale is the same. I recently solved a scale problem at a 600 gpm drinking water plant and distribution system for a reservation so I got a bit of a refresher on it.

 

There are probably other things that will work but this is my experience.