Red, 141 111 bytes
func[n][until[s: collect[loop n[keep random/only"LRK"]]parse
rejoin[s s][any[copy t skip opt t ahead not t]]]s]
func[n][until[s: collect[loop n[keep random/only"LRK"]]parse
rejoin[s s][any[copy t skip opt t ahead not t]]]s]