I am receiving many request to repair Clamshell (28c, 19bII, 18b) or Pioneer-type (42s, 17bII, 32s and many more calculators). Opposite to the previous models, these were built NOT to be repaired. The parts or the body are thermo-soldered, and opening them means typically breaking these bonds - which are quite difficult to repair in an aesthetically correct way.
There are some websites that talk about this. Most notably you can see repairs for a HP17bII here:
And here also (about a HP42)