The fix is to toss the stock prop and to replace it with a zip tie.
The biggest problem with the 70-73 seat prop is that it requires two hands to use. With the zip tie, you can flip the seat up or down with one hand, just like 74-79 seats.
Other problems with the stock system (at least in my experience) is that it is fumbly, it doesn't hold the seat up very securely, and you have to carefully tuck the latch in when you let the seat down.
Try it! I've been using the zip tie for a while now, and it is great. I use the area under the seat to store my riding gloves and a couple of reusable shopping bags, so I am very frequently lifting the seat up, and this is real minor hassle eliminator.