My 1997 Cherokee 4l (with 54k on the clock) started to have lower oil
pressure when hot.  Always greater than 3 bar when cold, but can drop
to 1 bar when hot.  Oil was clean and less than 4k old but I changed
the oil and filter (or the local garage did), but with no change.
Still low when hot, and often doesn't quite get to 3 bars at cruising
speed when hot either.  I don't know the oil used, but it was Castrol,
and probably a 10W40.  I would normally blame thinning or old oil, but
this is unlikely to be the case.  I'm a careful driver, never over
revving when cold, and treating it reasonably gently, especially when
towing.

Is the failing pressure sender fault as often posted here likely to be
a problem, or is there another likely other source?

Car has full service history and one previous owner who I've spoken
to.  He reports that he always had it serviced regularly whether the
mileage was due a service or not, hence the book is stamped to 78k
with only 53k when I bought it.