O.K., I have a tech here trying to replace both (with the upgraded version as to the transducer) and we are pulling out hair out trying to figure out how to access both of them for the job (and yes, I know it’s 4:30 a.m.). 
Anyway, the Jag workshop literature for XJS, not surprisingly, states to just open the hood, disconnect the wires, twist off the old ones, twist on the new ones, replace the wires, and done. 
Looking at that part of the engine, it is obviously NOT quite that simple.
The closest explanation of the procedure I could find in the archives is this one re: a '93 XJ40. Being that both models use the AJ6 engine, I would think it would be close enough (?) 
This post is for future archive reference.
In the past, I’ve only replaced oil pressure senders while
replacing blown head gaskets. With the intake manifold
uninstalled, swapping the oil pressure sender is simple.
I’ve been living with a bad transducer for a couple of years
and finally decided to see if it could be swapped without
removing the intake manifold. Guess what? It can!
I began the replacement process by removing the air filter
housing top and bottom. I then disconnected a number of
electrical connectors near the throttle body and unbolted
the items mounted to a triangular bracket bolted to the
front end of the intake manifold. I believe one of the
devices mounted to this bracket is the blue EGR solenoid.
Two fuel lines also clip to this bracket, so I carefully
undid the plastic clips which become brittle over time and
are easily broken. Now the fuel lines could be moved a
little from side to side to help me gain access to the oil
pressure sender.
I disconnected a wire-reinforced hose from the air pump and
tried to disconnect the other end of the hose, which
connects to some plumbing that sits right in front of the
oil pressure sender. Unfortunately, I just couldn’t get
enough prying force under the end of the hose to remove it
from its fitting, so I had to leave it in place.
I laid a flashlight where the air filter box normally sits
and positioned the beam so it shone on the oil pressure
sender. I could now reach under the remaining hoses and the
intake manifold and put my right hand on the pressure
sender. I could also reach in from beneath the thermostat
housing with my left hand and also touch the sender. After
considering my options for removing the sender, I decided
this was a job for a crow’s foot wrench.
I tested wrenches on the new oil pressure switch and found
the nut to be 7/8’’ or 22mm. I installed a 7/8’’ crow’s foot
on a 3/8’’ flexible coupling, to which I then affixed an 18’’
extension.
Holding the crow’s foot in my right hand, I snaked it
through the hoses and under the intake manifold. Then,
looking down through the intake manifold elbows, I slipped
the wrench around the hexagonal section of the old sender.
Unfortunately, the 7/8’’ wrench was too big. I tried again
with a 3/4’’ crow’s foot and it fit perfectly (19mm might
also work but I didn’t try it). With the wrench in place, I
then used a ratchet on the extension to loosen the old
sender. Once it was loose, I removed it by hand.
Installation was the reverse, but I had to use the 7/8’’
crow’s foot wrench on the new sender, which is the revised
‘‘switch’’ style rather than the original barrel-shaped
‘‘transducer’’ style I removed. To reduce the likelihood of a
future oil leak, I put a small amount of black RTV silcone
around the base of the hexagonal sender head after
installing the washer, being very careful not to get any RTV
near the sensor tip where it could interfere with proper
operation.
Another task checked off my long list of things to do!–
Don B : '93 VDP : (ex-'88 Sovereign)
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