I agree with all those that suggest you be compensated for either you doing the work or giving someone do it. Perhaps if you suggest that, they will gladly accept it.
Few years back, I bought my 3 cyl, 60 gal compressor from Northern Tools. The oil drain plug leaked and no amount of tape or caulk or anything else would keep it from drizzling oil down the side of the tank. Called them, explained the issue in a nice manner, they sent me a new plug. When that didn't work, the guy said if you don't mind changing out the pump unit, we'll just send you a whole new one! And just keep the old one in case you ever need any spares. I said sure, thank you! All new pump with pulley came about 2 days later. Took about 45 min to swap. Kept the removed pump cause you never know!
And of course with that service attitude, I buy from them without hesitation.