I heard about the Soviet slime stuff but like a lot of things Soviet, they simply ran out of money and the residue was as beautiful to a hunter as an oil slick. The idea was to allow itself to be trailed, clean...then emit the coating and slow down. The trailing sub is then un-able to feed the coated signal into it's database - supposedly. Norman Polmar's tome on Soviet boats goes into it briefly. But like he also muses, most NATO nations may not have had tons of subs, but they had tons of sub hunting aircraft! So the slick was easily picked up.