I have owned an S1 33 for about 15 years so I have a fair idea about what things go wrong with them. I just recently bought another and was pleased to see the front suspension rails repaired where they crack.
However, upon replacing the header tank, I noticed a crack in the inner guard which I have never seen before. Closer inspection showed a couple of cracks and upon removing the water reservoir on the other side, even more cracks.
I checked the other car and while not as severe, the cracks were there as well so go out and have a look and see if you have any.
Where to look: remove the water reservoir and look at the drivers side inner guard, near where the steering passes through the inner guard. Look near where the front brace joins the inner guard.
Passengers side, look at the bonnet stay on the inner guard and where the steering passes through the inner guard. In one car, the crack extended about six inches. In the other maybe an inch or so.
Both cars were affected and another one I looked at earlier was also affected. So it appears as if this might be fatigue related and common to this model. These are the worst cracks, but the whole inner guard is fatigued.
Passenger side where the steering passes through the inner guard. Nasty.
Drivers side where the steering passes through the inner guard. Normally obscured by the water reservoir.
Drivers side top opposite the bonnet stay.