Can't seem to locate the termination of the rear sunroof drain holes on a '92 wagon. According to the FAQ there should be visible plastic tubes under the side rear compartment panels but I see nothing like that there. Would this apply to earlier 740s, changed later on the 900 cars?

To the best of my knowledge the 740 and 940 sunroof trays and drains are the same in both sedans and wagons, and the FAQ is correct in describing the drains and locations. In wagons, I don't recall that the C-pillar drain tubes are visible from the storage compartment area, you would need to remove the side panels around the wheel well to find them.

In one case for me, tree needles caked in dirt were blocking the corners of the sun roof tray and obstructing the drains plus some debris extended a little into the drain outlets. The procedure for me was to fit a length of decent diameter (like 1/2") clear vinyl tubing to a vacuum cleaner crevice tool and feed it to the corners of the tray to suction up the debris while breaking them up with a length of coat hanger wire.

As tempting as it was to try reaming the drain tubes clear with the coat hanger wire, as James mentioned you risk pushing the drain tubes off the outlet nipples and turning this into a major project. Best to use a fine stiff wire like James suggested, preferably from below under the car if you can find the ends of the drain tubes, otherwise work from above. Extract what you can then try running a little water down the drain to flush things clear, parking the car at various angles to do one corner at a time. If you can locate the ends of the drain tube underneath then you can try reverse flushing with little compressed air. Just don't use compressed air from above and accidentally blow the drain tubes off as James noted.

From the factory, the drain hoses should not be kinked or pinched to restrict flow, however over time and with people prodding around, the hoses may become wedged into crevices and slightly pinched in which case you may need to start pulling side panels so you can get at the tubing.
--
Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now

How did you try to locate the drain holes? Did you climb under while someone poured water in the drain? If the drain is completely clogged, this will not work.

I had regular problems with the trunk drains in our '90 744TI - in the sedan, they can be found at a location about 6 inches behind the rear wheel well - incidentally, I never looked for them under the car - I could clearly see them inside the trunk when I removed the inner panel of the trunk

I think that they end above a lip under the bottom of the fender.

In my car, the problem was a plastic fitting at the bottom of the drain hose - the fitting was the same size as the hose and the hose was pinched in order to make it fit inside the fitting - this reduction in hose size caused debris to get caught, clogging the hose.

I suggest that you look inside, under the top of the spare tire well inside the fender. You may find the hose and a fitting. Does your wagon have small covers on the side of the rear floor as a 745 has?

My solution was to check the drain every month or so by pouring water down the drain and see if it came right out the bottom. I had to check the drain often because the rim around the trunk was exposed to a lot of debris - I even had to check the front of the trunk seal as well. Your sunroof seal, leaky as it is, should keep most of any debris out.

I got a piece of wire with glossy, high temperature insulation - this wire was flexible, but too stiff to kink. I made the wire about a foot longer than the distance to the bottom of the drain ( I did this when I had the tube off the fitting ) and marked it where it was inserted in the drain fully so I knew where to stop.

If the test water did not drain quickly, I would snake the drain - this opened it up.

In my car, there was a pretty sharp bend just below where the drain started, I had to bend the wire a bit at the tip to get it started.

You could blow the drain our with compressed air, I would worry about disconnecting it internally and having a bigger problem.

I know nothing about 900s If you cannot fond the tubes and fittings, you might try snaking them anyway.
The first time I tried to snake them, I had to perform multiple water tests and snaking to clear the drains.