Darrell (cook_dw) started an excellent thread on original paint and interior preservation here:
https://www.yenko.net/forum/showthread.php?t=133473
He mentions several products and techniques that worked well for him and others.
My experience with the Meguiar's #7 on darker color lacquer paints is that it makes a huge difference. Depending on the level of oxidation you have, you might have to use a more aggressive technique like buffing with #3 first to get the paint to a condition where the #7 will work best. These are proven old school products that have been around for decades and still work well.
I tried his recommendation on using an Oxy Clean solution and brush to clean the grain of an original vinyl top & interior and it worked well, but as Bill stated I also have had good luck with Simple Green - and it is a little friendlier on other surfaces.