Non-Polarized Electrolytic Capacitor Replacement
Several solutions
1) put two back to back series capacitors of 10uF/35V (negative with negative)
2) one polyester 4.7uF 40V like red WIMA  (have similar small size)
3) buy a bipolar or NON polar electrolytic capacitor from a catalog distributor or better audio components or ebay. They are still selling them.