When that lens first came out it lacked a focusing motor; then they revised it and added the "S" to denote "silent wave" motor.
The copy I have is the one without the motor; but the F5 I used it with most has a dandy motor, so the thing gave me excellent service; I've heard the one with the internal motor is a bit faster to focus, but it would have to be "quick" to be any faster !
For what it's worth, the lens in either config, is known to be a "brute", very few problems; I've used mine a lot, even use it now and then on my 300s with great results. I guess anything that's made to such precise tolerances internally can get "gummed up", possibly by dust infiltrating ? Im thinking, I'd try contacting a few repair places, describe the "issue", see if if they can give you a "ballpark" estimate to have it "looked at".
I bought a LOT of pre-owned lenses back then, had extremely good luck with all but one of them; I bought an old manual focus f4/105mm Micro Nikkor from this "schmuck"........"like new" it was ! ("supposed to be"); when I received the thing, it honestly looked like someone had used the front end, "around the objective element" to drive nails with ! even has a damned visible chip in the objective ! This was all back way before I ever even thought about digital, and had to buy my Velvia 10 rolls at a time from B&H, so I never even tried to take a picture with the poor beat up thing; went "round and round" with "the schmuck", via eBay, finally got something back, (can't even remember now what).............here's the funny part; after I had the 300s for over a year, I was telling someone about my ONE "bad deal" on ebay, and he ask me, "does it even work" ? It got me to thinking.........hell, I've never even tried to take a picture with the thing ! So a day of two later I spotted a bald eagle circling around over the neighbors pasture, ran in grabbed the 300s and the 80-200, and the damned "door stop" micro was in the bag; the eagle got too far away, so because I wasn't "doing anything", I decided to satisfy my curiosity, mounted the micro, set the body to "M", and shot some leaves, pebbles, etc................the pictures are "tack sharp" ! I was dumfounded ! (still am)
What I'm trying to point out..........it's actually much easier than most would imagine, to get good lenses, buying used; 99% are honest about condition.........if you get a BUNCH of great deals, and you get them cheap enough, you can save so much, compared to new prices, that a "bad egg" now and then don't matter so much. ( At least that's the way I think about it ) There IS
very definitely a WHOLE LOT to learn about buying stuff on eBay, (or anyplace else "used") overall, I've had great luck.
(BTW........when I got my f2.8 / 80-200.........the Chinese guy I got it from left a brand new Heliopan 77mm circular polarizer on the thing ! (I even offered to send it back to him ! ) "No no.....no send back" ! So eBay isn't all bad ! (neither are most sellers)
Hope you get that lens straightened out........good luck !
Stupidity: Doing the same thing over and over again and expecting a different result; Albert Einstein