Cold spot

It is a Pelitier array. If it doesn't cool at all, it is likely a bad Peltier. The Peltier is clamped, as I recall, to a heat sink which runs the width of the instrument. The heat sink has fins that are visible through the grills on the front, on either side. There may be a tunnel to the rear, through which air is drawn by a fan. The TEC5 has such a fan in the rear - I can't recall if the TEC4 does. It might have a fan directly under the cold spot. Clean the fins, on either side, as best you can, and blow out all of the dust. If there is a fan in the rear (or underneath), clean it, too, and blow out dust from that direction. After cleaning, if it still cools some, but not enough, it could be that the Peltier no longer has a good thermal connection to the heat sink. This would involve a lot of disassembly, cleaning, and reassembly with new thermal transfer compound, RTV, and new adhesive insulation. It's a big job. If you can improve operation a few degrees by cleaning, that might be enough to satisfy the histotechs. I don't think the temp spec for the cold spot is much lower than +10 or +15C.

Thanks.
Toaok it appart. There was a lot of wax in there. Cleared it out. Peltier seemed to still be  working. Used a therma 'mat' rather than the paste. Put it back together and its doing the same thing. Gets cold when you turn it on, but then gradually doesnt keep cold as well. Might check to make sure I have it seated well, but it might be a lost cause

The ability of the heat sink fins to shed heat will be affected by ambient air temperature, the temperature of the hot surfaces nearby (don't set them hotter than necessary), and air flow - ensure there are feet on the underside of the unit, to raise it up off the benchtop (I think there are grates below those fins, so air needs to be able to flow).
Maybe the power supply that supplies the Peltier is sagging, too.

The cold spot may not get impressively cold - but it doesn't need to be very cold, to be useful.

Good luck.