I bought a rebuilt MC for both my 300D's at Autozone (~$40), but they don't come w/ reservoir. You can buy the rubber grommets at the vendor here. The reservoir level sensors (2) are a simple 2-wire on-off switch, so can check w/ a multimeter. You should hear them rattle as you shake it. If no rattle, try cleaning by pouring in ethanol and shaking around, then completely dry it. If the brake light wasn't coming on, the bulb may be bad. The rubber caps are resilient for testing. Push down and level warning should light.

Your booster if probably OK. I had brake fluid in both mine, so removed and poured out & absorbed w/ rags. I now use silicone fluid, so no more corrosion. No white smoke, the fluid would just go out the vacuum pump, but I can't see the the level reaching the vac port.