Ford Repair: Oil Viscosity, valve stem seals, extreme cold weather

Question
I own a 2002 Ford Explorer 4.6 V8 with ~ 83k on the clock.  Recently, I had an oil leak repaired by my local indy mech.  He replaced the oil line mounting plate, a plastic part that mounts between the block and the lines/filter.  Since the truck has been noisy on the top end @ cold start up, almost like leaky valve stem seals.  Goes away after a minute or so.  Oil seemed thin on dipstick (5w-20 as recommended by Ford)  so I took it back in.  Indy mech says it's because Speedy Lube uses bulk oil, and you always get thin oil from bulk.  I don't buy it.  I suspect that formulation is same whether bulk or in quarts.

Question:  Should I be considering 20W-50 at this mileage on the engine?  Anything else?

Answer
Absolutely not, do not change viscosity. Your engine is designed for 5w20, so not use anything but that. It is basically 20 weight oil at all times, and 5 weight during extreme cold weather. Your mechanic may be onto something. It is common knowledge that "speedy lubes" use whatever is available, and cheaper. Their is no way to find out, other than their word. And I personally don't trust them. The only true way would be to add the oil on a quart by quart basis. As far as the noise goes, did it start right after your indy mech replaced the parts, or after the next oil change at the "speedy lube." The answer to that question, will be the answer to your problem.