abenton

Had some noise from the rear end so changed the diff oil. Suprised to find oil drain plug didn't work but as I found from threads removed and replace through fill hole....

Question... shot some air into drain hole (thought it might be plugged up) and could hear air bubbling on the fill hole side (with fill plug removed). If this is just a diff case bolt why the air passage to the inside??? Also left the car sit over night with rear drain (?) bolt and fill bolt removed and in the morning some oil had drained from the rear bottom drain (?) hole.

Is the '87 unique or did Elvis stop by and spill some oil to leave me wondering WTF ????

WVZR-1

There is no "DRAIN" plug on the differential from OE/GM. Post up a snapshot of what you "thought" was a "DRAIN".

Some use a lower cover bolt, drill from the differential to intercept that bore and use it for a drain but it's not particularly effective.

If you removed a cover bolt assuming it was a "drain" you've likely erred. If the cover to differential seal wasn't very good to start with removing a cover bolt likely just let the seam leak. Your blowing air into it likely aggravated the situation OR maybe you're just "trolling"?