Automotive rubber replenishes are useles. It's made for a different type of rubber. This topic comes up every 6 months or so.
I went to the trouble many years back asking advice of experts from multiple museums in rubber preservation. I posted a report on the old VAME site. I also spoke to many engineers who develop automotive rubber revival products.
The answer is grim. There is NOTHING you can do. Museums have struggled with preserving rubber products for decades. Unfortunately the rubber that our loved Action man and GI JOE wetsuits are made up from cannot be saved. They were never made to last forever BUT worked sensational for the lifetime of our childhoods and was brilliant. My favourite pastime playing in the pool with my Action Man diver and Armoured Command jeep. The wetsuit was still folded up in the back section when I found my new reborn joy for the hobby a decade or so ago. Sadly brown and brittle.
Best advice is to keep it away from sunlight and air in a well climate controlled room. BUT DO NOT put them in airtight containers as the gases the rubber expels in its breakdown period will actually accelerate the deterioration. They have to be able to breath.
My conclusion was to give up buying good suits. I still have a few originals stored away as best I can that havent seemed to worsen much over the last 5 years or so. I got a guy in Brazil with original moulds to make 20 suits for me and 2 friends around that time. Black, Orange, yellow, different issue zipper variations. Even YKK zippers. They still are like new. Love em.