This writeup is for the Third Gen Subaru Leone, a.k.a: "Loyale" or "EA82" etc,
but the ideas given here might work, with some changes, to other vehicles as well.
Have you ever felt the Seat on your Subie like a Rocking Chair?
The Subaru EA82 GL has a Complicated Air Conditioner Distribution Design, which includes a couple of Ducts under the Front Seats, one ends there to deliver Air to the Rear Passenger's Feet, and the other Duct delivers Air to the Rear Doors' Windows; this last Duct, passes through one of the Front seat supports, weakening its structure somehow.
The Weakest Front Seat Support, is the one located at the Rear of them, next to the point where the Seat Belt Anchors; there is the A/C Duct passing in the middle of said Support. I've seen some local Subies with those Supports Broken, especially the Driver's side one, and the owners didn't knew the reason why their Driver's side seat was loose and / or way too much reclined to the Back... (when said support is not only Broken, but also Deformed for using it like that) ...I Bet that many Subie owners could have same issue on their cars, without even knowing, nor completely noticing it.
So, that support on the Driver's Side in my Subaru "BumbleBeast" has broken for the Second Time... I Know: I am a Big Guy, 6' tall and over 110 Kg driving an Old Subie Wagon with Hardened "Reinforced" suspension, so the autogenous welding I did a couple of years ago to simply put that broken support together, will never last too much... so this was the Perfect Time to Reinforce that Seat Support and permanently getting Rid from that problem.