The weep hole is actually an intentional little hole in the w/p housing adjacent to the impeller shaft seal. If the coolant starts to "weep" past the seal, it exits through this hole. This is an indication to you that w/p seal failure may be imminent, although they will usually weep for a while before you get any serious leakage. But I wouldn't count on it.
Go ahead and replace your water pump at the first opportunity. Then as long as you've got the cooling system drained, you might want to consider changing to Evans waterless coolant. It's a non-aqueous propylene glycol coolant with a boiling point of 375 deg. F. That means it runs at essentially 0 psi, putting less stress on all parts of your cooling system, from radiator to hoses to pump to heater core. I put it in my '86 300E in July '02 and then loaded all four of us, our luggage and a 10' popup trailer and headed up to Anacortes, WA from So. Cal. The first thing we hit was the Grapevine at about 1 pm and over 100 deg. temps outside. The car never even thought about getting seriously overheated. As I recall, the temp guage hit 110 once on one of the steeper, longer inclines but it came right back down as soon as it leveled off a bit. I'm very impressed with the stuff. We put on over 2500 mi. during the trip and I've rolled up over 20k miles in the last year. I haven't had to add on ounce since I put it in, and I don't even worry about overheating in traffic at all. The only hassle is getting all of the remaining coolant/water out of your system, but it's really not that bad. I'll describe what I did, if you're interested. The coolant is about the same viscosity as MB coolant, so no changes are required to any part of your stock cooling system. The price is a little steep at about $25/gal., but considering that they claim you can leave it in there for 300-500k miles, I think that it's quite cost effective. Here's their web addy: http://www.evanscooling.com/main31.htm
I know this may start a flurry of posts pro and con, but I'll be more than happy to answer anybody's question about my experience with the product.
disclaimer: I have absolutely no connection with Evans Cooling. I'm just a very satisfied user of their product.
Hope this helps