Well, the freeze plugs all hang out in pretty much the same environment. Aside from the two on the back of the block... so, if one of them is rusting out, it really wouldn't surprise me that a bunch of the others were as well..... You can get a whole set pretty cheap, if you find another one leaking, just go thru and replace them ALL.

 

It may be politically incorrect to suggest something easy, but when all else fails, you might try www.barsleaks.ca I did a fair amount of label reading & the Rhizex pellets seem to have more going for it than the regular clay based or aluminum particles etc. Was used to stop a leak in a Nautilus going under the North Pole! They all recommend doing a coolant flush first so the stuff will bond better.

Nitro, am wondering if your area of Michigan has salted roads? This may or may not be a factor in what's going on there, along with the colder climate. Steel doesn't like salt...

fwiw: just replaced the water heater on my van & then discovering a pinhole leak on the upper left of the timing cover, realized that there wasn't time just yet to replace the timing cover & do a timing set changeout.....
drained all the coolant out, removed the two longest bolts on the left of the pump, blew air through the coolant system from the radiator cap, ( pinch the overflow tube) & found the lower left bolt has a passageway to the outside. After the air coming out got drier, I stuffed some cotton rags in there until they came out dry. Then, plopped some ultra blue in the hole, coated the( cleaned) bolt with more of the same, & retorqued them. Sat to dry overnight. No more leak.

 

Yep, Michigan is on a salt mine - literally. Yep we have lots of salt in the winter. It rusts everyhting. I just got the truck a week ago from a friend for my son to use for work. I didn't pay much for it, and fixing it right is the only way I do things. The PO was just dumping water in it when he needed to use it plus it sat for the past 3 months. I imagine all the expansion plugs need replaced like someone earlier said. The latest leak is on the passenger side block, middle plug. Of course it's right behind the motor mount. It's not much for a leak but will need attention. Since I just put a new radiator in, I will not add any kind of stop leak.

On the timing cover, there are actually 4 bolts plus the top 2 outers of the water pump that go right into the cooling chamber of the block. I used RTV on all these bolts. My timing chain had an unbelievable amount of slack, so changing it and doing the cover was a god thing. The truck runs soo much better. BTW my timing cover gasket was blown on the upper part on the passenger side inlet for the water pump. I was tempted to just do the bolt as suggested. Again, glad I did whole thing now.

I did the magnet test on the plenum as well. Still original at 235k miles. That will be my next job, plus a tune up.