Never heard of an expansion valve going bad on our cars, curious what symptoms you are getting that you think you need to replace it. It’s a very simple device, made of a sturdy non-rusting metal and with no moving parts, it’s also in a very well protected area away from the elements or anything that can damage it. Regardless, on the late 944 (I’m sure the 968 is identical) you can get to the expansion valve by removing the blower fan assembly. The assembly is held in place by six 8mm bolts and some goop, to remove it you have to remove the bolts, pry it off the goop and disconnect one vacuum line and one electrical connector. The expansion valve sits under the fan assembly on the right-hand side of the car.

My AC compressor was making a grinding noise over 3k rpm for a period of time so I only used it sparingly under that rpm load but occasionally still heard it grind. Then one day no more grind and no cold air. Tested pressure and compressor is dead (no change when on or off although clutch engages). Not sure if it grenaded or just went out but from googling best way to check is by looking at expansion valve as it would have metal shavings in it and need to be replaced. Also would mean I would need to flush system in which case the valve has to come out to perform the flush. Bit of a nightmare vs just replacing compressor and drier but if there are shavings in the system I’ll be doing all this work and money again. Curious is that logic sounds right to those of you here or if I can check for shavings another way?

Expansion valves do have moving parts and do fail occasionally.
To the OP, just replace the dryer along with the compressor and call it a day. The dryer should have caught any debris coming from a failing compressor.

Marc is correct, my bad. I’ve been working on too many “modern” systems lately which use orifice tubes (no moving parts) instead of expansion valves.