I gave my XJ308 a power wash. However, when I took the car for a drive to dry off the water, water poured onto my right foot (RHD car) when my foot was on the accelerator. Additionally, an error came on the dash, "Restricted Performance" and the gear box warning light came on, but no issue on revs available or changing up or down, Any idea where this leak is? The door seal looks good and I can't see anything out of place under the bonnet/hood.

 

have a look under the grey plastic panel at the base of the windscreen, they are known to accumulate dirt and leaves under here, and it then causes the top of the bulkhead to rust through.

 

Agree with Andrew. I had water infiltration on passenger's side after heavy rains. Turned out the 'drain' at the bottom of the windshield was clogged. Wasn't very difficult to clean out, and never had an occurrence again. To access, remove wiper and then the plastic 'drain cover' (few hex bolts). There's a drain hole in there somewhere ;-) Good luck.