Flash Car Wash system - similar shampoo?

[Stuart Davidson]

Apologies if this comes up regularly. I sense it might but can't find anything having trawled back quite a few pages.

I've got one of the old Flash Car Wash systems that I use quite regularly. Bought up a job lot of filters and shampoo when they stopped making them. Still got quite a few filters but have either lost or used all the shampoo!

Has anyone been in a similar position and can recommend a suitable replacement shampoo that's not so thick to gunk up the chamber!