The first thing to do is put the machine into the switch test, and run a ball around both ramps. If both switches you mentioned register, then they are both fine, and just means that those shots haven't been made in around 50 games.

If they don't register, then check the following switches to see if they work:

Shield Popper
Left Shield Target
Right Shield Target
Shield Up
Shield Hit

If some of the above don't work also, then check the wiring under the playfield - you probably have a broken wire.
If all of the above switches don't work, then you have a switch column fault, and this will be somewhere on the driver board under the playfield, but may be a broken wire.
If all of the above switches work, then the two you mentioned are faulty, so first check the wiring for broken wires, but you may need to replace them.

Unfortunately, the manual I have here does not list a part number for either of the non-working switches, so I'm not sure exactly what they are without going out to my workshop and looking at the SWEP1 I have here...