I changed mine out, you can get one at the local parts store. Even though the switch part is seperate from the pressure part, with a crack in the plastic, if the diaphrame on the pressure side was to give or leak, more likely to have an oil leak out it. Also if it did start leaking out that crack for some unknown reason, could even increase chance of sprayng a fine oil on the hot pipes when riding and thus possible fire.
Recommend when you get a chance, to take it off, go to NAPA and have them dig through their parts to get a simple N/C Oil Pressure Switch with approx 5 psi closing spec. Would recommend you have the old one in hand when you do so that you can make sure the threads match up and the size.
If I recall I paid in the $10 range for mine. A local HD shop may also have one that will work, though most of the HD shops I have been to lately will not even attempt to find you a part unless you give them a make and model of HD that they can check their books against. I guess the only know how to look at a part list anymore and not like some of the old guys that could look at a part and knew what would fit or would cross reference.
Was frustrated as hell one time when I was just looking to get mount bushing for my split tank and kept telling the guy Fat Bob Tank. He couldn't figure it out and said they had none, so I went through his Drag Specialist catalog and found the bushing and what were some of the models they listed, gave him a model and he found bushing right away.