I
Have you taken all the windscreen chrome off and had the widow resealed
Thanks Robin - so now I have a general idea of where you showed the first photo - I will try to locate any area where items (in the engine area) go through the bulkhead on my LHD XJS and enter the driverâs footwell area - Tex Terry II 1991 XJS V12 Classic Coupe, !986 XJS V12 Coupe, 2/5/2020 1717hrs EST USA
The entry point for my water ingress was a hole on the other side of the firewall inside the fresh air plenum.
Lost here - you are saying that the water wetting the driverâs footwell area, came from water in the fresh air plenum area? Going backwards then, you found a hole in the firewall sector of the fresh air plenum - then you found the rust area in the engine area wall - just not following - Tex Terry II 1991 XJS V12 Classic Coupe, 1986 XJS V12 Coupe, 2/5/2020 1734hrs EST USA
Yes thats what I believe was happening.
Ok - I will try doing this back direction check (once I am mobile again) from above the driverâs footwell area (LHD) to see if I find any indication of water entrance, and then I will post my findings - Tex Terry II 1991 XJS V12 Classic Coupe, 1986 XJS V12 Coupe, 2/5/2020 2146hrs EST USA
O.K., before leaving last night, I stuck my hand under the rocker panel area and felt all along it upward for drain holes (I am too big to get down on the ground and look upward, and it was way too cold anyway! 
). I didnât feel any holes in it. Are you sure the face-lift models should also have those drain holes? 
Canât say if facelift models have them, but I would think so - if you have access to a hand mirror, place it on floor and slide it along, from front edge by wheelwell to back wheelwell and you should see the drain holes that are described in the body section of my manual. Tex Terry II, 1991 XJS V12 Classic Coupe, 1986 XJS V12 Coupe, 2/6/2020 0138hrs EST USA
Hopefully the following link will work: http://www.jagrepair.com/JaguarXJSElectricalOBDIIcodes.htm for you to gain access to a PDF of the sill drain information - scroll down to the Jaguar XJS 1989-1991 Coupe-Convertible Body Enhancements section - then scroll down to the Sill Drain pages (first section) and you will see description and pictures of the drain holes - this section also describes the A post and fender drain - Tex Terry II 1991 XJS V12 Classic Coupe, 1986 XJS V12 Coupe, 2/6/2020 0221hrs EST USA
Thanks. Will check it out thus, and if I can find my dang LizardCam maybe employ it in the endeavor, too, possibly venturing up into the holes once found and take a look around in the area under the sill plate. 
Hello Rex647 - the reseal of the windscreen is on my list in my process of making sure I have stopped water flow in to the cabin area - as I find, seal and test each area for leaks on my 1991, I will try to remember to post here - Tex Terry II 1991 XJS V12 Classic Coupe, 1986 XJS V12 Coupe, 2/7/2020 0224hrs EST USA
Hello AttyDall - in that same section (the Body Enhancements) of that link, there is detail concerning the door seal placement, with a statement regarding special attention to the section near the A post deter water leak - the same link also contains sections for your 1994 so hope this helps - Tex Terry II 1991 XJS V12 Classic Coupe, 1986 XJS V12 Coupe, 2/7/2020 0244hrs EST USA
Thanks. I may actually try tackling door seal replacement, and that may very well be the source of the problem. I have never tried it before on any of my Jags in the past b/c of that crazy method that has to be used in installing them. I know Jag gives a description and specs in their online factory service literature on how to fashion a hand tool to (supposedly) help with the installation, but donât know if anyone on here has actually done that. Iâve read on here of all the other âimprovisedâ tools for the task, inc. using dulled-end screwdrivers to drive the seal home in the groove, but something tells me it will still come down to me using âtwo sore thumbsâ, a lot of time/patience, and a lot of soapy water (some say use saddle soap? others say use a lot of WD-40 spray?) to aid the chore. 
One thing I did read, was that there is a particular sequence for the door seal installation so that it will seal correctly - please advise if you do get a good seal - Tex Terry II 1991 XJS V12 Classic Coupe, 1986 XJS V12 Coupe, 2/7/2020 0258hrs EST USA
Yes, I made a note of that (literally). I thought I had read sometime back in a Jag manual that you are supposed to start in the rear upper corner and work out in both directions from there, using painters tape to initially hold the seal up while you work it. However, the directions here say to do just the opposite!
That bit of directions does make a difference of ease of install and finding it in print does settle difference of garage mechanics ways - I am sure you will probably correct your water leak problem before me, so I will keep checking in for your results - Tex Terry II 1991 XJS V12 Classic Coupe, 1986 XJS V12 Coupe, 2/7/2020 1819hrs EST USA