You're right that Toshi doesn't play on the 4th and 5th albums - he returned to the band immediately after the 5th album was released. In an interview with Toshi in Rokku Gaho no.5, he gives the following explanation:
"I was tired, tired of Zuno Keisatsu... Tired of the music. I originally liked our freer stuff better, so I told Panta I was leaving the band. In the end I took about a year off."
It seems that in that year he did some free stuff with his own Electric Percussion Group, and he played with Taj Mahal Travellers for a while.
The other members on the 4th and 5th albums are:
Makaino Koji (keyboards)
Takebe Hideaki (bass)
Tanaka Kiyoshi (drums)