Morris Minor Owners Club

I found a source of water leaking into the box section under the rear seat that I haven't seen menioned anywhere.

1968 2 door, rubber seal round the passenger side rear window is in a bad state. Water seeps inside the rubber, drips off the panel onto the plastic covering the wheel arch, runs down he side of the read seat squab onto the floorpan and into the box section where it stays forever, until one day you take up the rear seat and find a couple of pints swilling around.

Luckily the box section has something like wayoyl in it so there doesn't seem to be a lot of rust. A VAX is useful for sucking out the water, then gentle fan heater to dry it.

I've put in some more waxoyl and used a sealer on the windows rubber. Don't know if it has worked yet because it hasn't rained since.

So beware! The only indication there was a leak was the occasional drip visible inside the window during wet weather, which my wife didn't think was important ...

, until one day you take up the rear seat and find a couple of pints swilling around.

more likely is that one day you fail the MOT due to corrosion around the spring hanger.
The rear window, and rear side windows are all probable sources of the water entry. It's hard to find a cheapish Minor that doesn't have this problem (leaking windows never seem to get fixed of tatty cars - people end up spending 10 times the price of a window rubber having the car welded every year).

On many cars the water leaks from this area into the rear footwells making the carpet wet. The waxoil in your box section has probably sealed the joint to the floorpan keeping the water under the rear seat - Hopefully that has protected the metal along the spotwelded joint.
One of the simple measures that you can take (as well as not ignoring any leak!) is to put drain holes in this area.

Here here, the Minors are woefully short of drain holes ,which also
act as ventilation points, so drill some under the rear seat assembly,
some in the rearmost lowest level of the boot floor, and it is not often
realised that the factory drain holes in the sill bottoms are actually
about a quarter of an inch ABOVE the bottom of the panels so you
can have that much water slopping around at any time before it reaches
the drain hole level.

If you had as much as a couple of pints of water in there also check the rear window rubber as this is the biggest culprit in this area, its also listed as one of the check points when buying to lift the rear seat out to check for corrosion because in this area in can cost a lot to repair if rusted badly.