I can't push the back seat back into the position
 

I had to remove the back seat on my 1987 260E in order to gain access to the vaccuum pump. The seat comes out okay, but I can't put it back. The foam is just too thick so I can't push it far back enough in order to line up the the two red tabs. I wanted to put both foot on it and push but got no leverage in the cramped space.

Any tricks, tips I should be aware off? TIA

Go to Home Depot .....
 

and get two 80 lb. bags of Quikcrete mix. Lay in seat on top of old sheet or towels and see if that won't press the cushion down so you can slide it in. Then return bags to store for credit.