Megatron replaced the cell in my Master IV three years ago. I initially just wanted to order a new cell, so that I could install it myself, but they said:
Selenium photocells are all different - very individual, therefore, it is
important to first - choose the right cell to match the movement, and then
calibrate the instrument to give correct readings with the new cell. You
would need a specialist equipment to do that. We can carry out the repairs
for you (fitting a new cell, servicing and minor repairs & recalibration).
So, I sent the meter to them, the cell was replaced and the meter calibrated. It works perfectly now. Personally, I prefer to have my equipment properly serviced and calibrated, even though it often is cheaper to buy a "new" meter, or camera for that matter, on eBay. But then it's very easy to end up buying several meters before you get one that works properly.