There is a soak that lots of vintage clothing dealers and collectors swear by called retroclean. It's pretty gentle and generally gets good results. Available on Amazon or other retailers online.

Retro Clean Cleaning Solution https://www.amazon.com/dp/B006UD22K2/ref=cm_sw_r_apan_i_TTCXCBEZPRNS1Z7YAS8A?_encoding=UTF8&psc=1