I don't know of anything to put around joints for finding leaks but one thing I've used is a stethescope without the diaphram. Use the open ended hose to get right at the joints. Works in tight places and really helps when you're listening for very localized noises.
BTW...I looked at Home Depot for that grease and found two types, one says for ceramic seals also but I have no idea what the difference is in the two types. Got the stuff for ceramic and it seems like the right stuff so we'll see. Price is good too.
Al