Water Leaks

Bonnet Hinges
Check that there are rubber gaskets under the bonnet hinges (yes people do fit new hinges without putting a gasket on, probably because the old one had completely disintegrated and didn't know about it!)

Winscreen Wiper Arm Drive
There's also supposed to be a gasket under each of the chrome or plain metal bits that surround the windscreen wiper arm drive where it comes out just in front of the windscreen. These have probably completely disintegrated as well.

Windscreen Rubber
The most obvious leak and the hardest to fix is the front windscreen rubber. Water will be seen dribbling down the front of the dashboard at each lower end of the screen. It's possible to temporarily stop the leak by using a windscreen sealant, but the rubber will be so perished that the next time you wash the car more rubber will wash off and the seal will leak again. You can try Waxoil but this just swells the rubber until the white spirit base has evaporated. The only answer is to replace the entire rubber seal.

Windscreen Washers
Look for leaks in the tubeing from the washer bottle to the windscreen. Does ALL the water get to the windscreen?

Bonnet Rear Seal
There should be a rubber seal at the rear of the engine bay that makes a seal when the bonnet is closed. If this seal is missing water will be free to run down the bulkhead and through any one of the numerous holes that riddle the bulkhead/dashboard (soundproofing securing holes for instance). The only cure is to fit a new bonnet seal.

Front Guards/Wings
If new front wings have been fitted, how sure are you that any repairs have been done properly and that there are no blow-through holes where welding has been done? Check that the piping between the guard and the body has been replaced on early models.