No.
No. Looks like this is the kind of relay where you can take off the case. Remove the case, clean the relay parts and the case, reassemble it. Easiest to do when you remove the relay from the PCB first. Make sure no power is active while handling the PCB.
I have no clue.
Normally they don't. Maybe a residue from washing the PCB after soldering? Moisture from condensation?
If it ain't broke, don't fix it.
This explanation seems most logical. I knowingly used an "ice cube" type (removable cover) relay in an application which exposed the relay to the weather elements. I constructed a rain cover but it was the airborne particles that crept thru the minuscule openings. I was quite surprised how much dirt accumulated inside the relay's enclosure, so quickly, as to inhibit proper action of the relay. The removable cover made for easy cleaning. Most definitely de-energize circuitry before cleaning components.
Hmmm. Do you get this from the same store that sells headlight fluid and muffler bearings? Oh, wait! You probably meant something like Dow Corning Vacuum Grease or perhaps the heat-sink compound used between a semiconductor case and its heat sink...
