Hi Herb.
On the w123 chassis this is a
very common problem.
There are a few reasons and places
that can cause the leaks.
Look in the engine bay near the
hinges.
You'll see a "pocket" where the hinges
fold into.
See pictures.
These "pockets" fill up with debris,
leaves and/or pine needles and blocking
the drain holes.
When it rains these areas fill with water
and over flow into the cabin.
Also remove the battery and battery tray.
Take a close look at the fire wall because
there could be a hole there and letting
water in.
Next is the sun roof drains.
There are four, one in each corner.
The two front ones terminate into the
front doors near where the power wires
go into the doors.
If the hoses or the connections are bad,
leaks are the result.
The rear ones end in the rear somewhere
but I'm not sure where.
The wind shield is also a possible
cause.
The rubber dries and shrinks, this separates
the glass from the rubber causing leaks
in each lower corner.
Lastly the doors seals, although not realy
likely but not impossible.
Louis.