|Water dripping over
This is a particularly irritating water leak, but one that is readily observed - after all, how can you miss torrents of water cascading down your door trim so blatantly in your line of sight?
If you've never had this particular water leak, consider yourself fortunate, as it seems to be pretty common, and appears to get more prevalent as the rubber seals age, harden and flatten.
The aetiology of the leak is actually reasonably straightforward. The rubber seal on the A-pillar (the windscreen surround) has a water channel that allows water to drain through it and to vent harmlessly into the door shut face, and from there to the floor outside the car. This can all go wrong if the rain channel is blocked - often through compression between the door mirror mount (the wind cheater) and the A-pillar.
Obstruction of the seal water channel has a number of causes - on early cars, one of the commonest causes is a misaligned window - most often triggered by the collapse of the window stops. Another cause, nicely illustrated in the image, left, is misalignment of the door mirror support - or 'cheater' as it is often referred to as. On this image, you can see it's upper most point (1) is displaced outward from the windscreen pillar. Therefore, instead of the long edge of the cheater lying parallel to the A-pillar, it is divergent, being closer at its lower end, compressing the seal.
If you look carefully at the image, you can see what has happened to the weather seal - about half way along the long-edge of the cheater (2), the seal is pushed inside the cheater's free edge, compressing the drainage channel.
The consequent failure of drainage causes the water to seek another through path - often pooling inside, adjacent to the mirror adjusters, and running down on the inside of the door card.
The other problem that leads to leakage is alluded to in the first paragraph: old, hard and flattened weather seals. MGF/TF seals appear to last well - but after 8 or 9 years are usually past their 'sell by' date.
The Cheap Solution:
The cheapest, easiest solution is to employ one of Mike Satur's 'Sun Mate' covers - or a similar 'storm cover' from any one of a number of sources. These covers effectively form a tent over the critical window-door seal interface. Job done. But it does mean that every time you leave your car, you have to cover it. And worse - if you have to drive the car after a period of rain, you have to store a damp roof cover somewhere in the car. The ideal place is the front boot area - but it is a hassle if you are in a hurry to open the boot to pop the bonnet just to put the thing away... Better is to fix the underlying problem!
The "real" solution:
Previously, I have referred to a number of problems that can result in loss of drainage through the seal - and quite often you see all three contributing to the problem. In this eventuality, the best solution is to re-adjust the alignment of the windows and mirror cheater, and replace the weather seals that may either have become too old, or too damaged by misaligned window components.
Old Flattened seals
A potential, but usually temporary solution for flattened seals is to open up the drainage channel. One method that a number of enthusiasts have found to be effective is the use of a length of plastic piping (such as that used in aquariums for oxygenators etc). Inserted into the water channel of the seal, the collapsed section of seal can be restored to patency - to the benefit of preventing the ingress of water.
However, a more effective long term solution is to replace the seals with new. It is possible to make use of improved design weather seals from MG TF on earlier cars, as the windscreen surround and glass has effectively remained unaltered throughout production (1995-2005 - although the size of the side glass was altered in 1998 with the introduction of the Mk2 softtop and frame seals).
Replacement of weather seals is dealt with here.
The key to sorting this problem is to determine why the window alignment has moved from the usually water tight factory setting. The commonest cause on early cars was failure of the window guide/stop. Richard Eaton's replacement guide can be found here.
If the underlying cause has been rectified, the next step is to ensure that the window alignment is now perfect. If not, then follow the window alignment procedure detailed here.
Unfortunately, there is not a great deal of alignment adjustment on the window cheater. If the support bracket has become bent/distorted, replacement may be the only course of action. See more here.