jaysun23,
Sport King was a brand sold by Wards. Some were made by Ocean City. I'm not familiar with the Model 52, but of the other models I've run across they all fall into the $20 to $30 range of value in excellent condition. Any other markings on the reel might help to give it a better ID. But realistically, It was your grandfathers reel so that makes it priceless.
As far as maintenance goes, wiping it down with a silicon cloth and removing any dirt and old oil and then
lightly oiling the reel with a high quality oil like Penn's Reel Lube it all it should need. If the reel is very dirty soaking the parts in a mild solvent such as Murphy's Oil Soap and then brushing with a soft toothbrush should loosen any stubborn grime. I'd be cautious and dilute the Murphy's instead of using it straight, especially if there are any hard rubber or plastic parts on the reel.
If there are any screws you have to loosen to disassemble it make sure to use a good screwdriver that fits perfectly, like a gunsmith screw driver or a jewelers type. Don't force any frozen screws as this will bugger up the screw head and may even snap the screw. If the screw is frozen try a drop of Liquid Wrench and gently tapping on the screw driver.
If you can, post some pictures of the reel for no other reason than vintage tackle is pretty cool stuff.