I had the same situation on my 94 e320 and did the same to release them. However, I used a spray grease rather than wd40 that iis really a rust disolver rather than a real lubricant.

When the door is closed it pushes the pin into the lock mechanism. The real potential problem is the cable in the wheel well that connects to the foot paw that is held down when the seat cushion (for your butt, not your back) is in the seating position.

The more often you release the seat back, the easier it releases.

Bob

P.S. Although my Golden Retriever has lots of space with the seat backs up, he prefers when I fold one down so he can get closer to the front passengers.