Is your problem also occurring on the first score reel (leftmost)? Being the highest value it may not have a ninth position switch. That would give you an idea as to the 9th position switch causing a problem. If it's just one or two random reels on a 4 player game it's possible that there might be too much tension on the 9th position switch, but I've never seen such an issue on every single reel. 9th position does take more force to pull in all the switches but there's usually enough power as long as the reels and cams are clean. I've done hundreds and never replaced a single coil or spring. You might want to make sure that the EOS switch that breaks the current to the score reel coil, is adjusted properly. If it opens too soon, maybe the coil is letting go before getting a full stroke. You need a full solid stroke to push through that 9th switch stack.

No. Many factors involved. First it would be good to know what particular game although they all work similar. I see you have both Williams and Gottlieb.

I take them completely apart and clean everything and look for worn parts because that does happen. And a tiny bit of lube in only the places the factory used it. Sometimes springs have been modified or replaced with the wrong ones.

When put back together switch adjustment can be tricky. Too much tension can hold the reel at the 9 position switch. Sometimes the 9 position cam gets a flat spot that can hang things up too.

Low power can sometimes be traced back to a bad electrical connection somewhere. Relay is involved too.

People are going to chastise me for saying this, but I use WD-40. Most of the time it works, but sometimes it does not. Then and only then, I take the unit apart.
For Gottlieb Decagon units, I spray them in the center where the reel is attached and all joints. I hold in the coil then I spin the reel several times to loosen it up. Apply more WD as needed. Works almost every time. If the unit does not do a clean 9th position, on the Gottliebs I adjust the switches slightly until the 9th position gives a good clean snap.

I've taken apart a few WD-40 games. Must have worked for a while because it gathered all kinds of dirt and crud before it stopped working. The damage wasn't totally irreversible, but it sure gums up the thing and makes a mess.

WD-40 will cause the reel to gunk up eventually. Silicon grease where needed (metal on metal) and nothing else.

The vast majority of 9 position issues is switch adjustment. Not very often a spring or other mechanical issue.

Silicon or PTFE oil. 3 n 1 makes both in these little squirt bottles and you can get them at lowes. Works wonders. I put it on games that have sit for 10+ years and they break loose and work great.

Since the op is now mia, and we don't know what game he is referring to, I'll throw my tip on the later Williams score reels starting in the mid 60s throughout the 70s out there.

They are pretty simple in design and function, and easy to get working if they do hang up. Only thing I have had to do out of the ordinary, is sometimes the cam that drives the switch lever develops a tiny flat spot which results in a small point on the cam. A file can be used to round it off, and everything will work fine again.

I use tiny dabs of super lube on the cam and the post it rotates on after I clean them, as that is where it looks like the factory lubed them, but that old lube has long since solidified.

I cleaned a sticky score reel on a new (to me) Gottlieb 2001 last weekend. The sticking occurred at the 9-to-0 transition when the switch was exerting its highest pressure. But the real issue was old gunk (once lube) between the moving metal actuator of the score reel and the metal chassis of the score reel itself. The geometry of the switch arm was increasing the pressure on those gunky metal surfaces during the key switch transitions.

I kept taking out the score reel and cleaning those gunky surfaces with alcohol and Q-tips. I would put the score reel back in, it'd work well for a while, and then some additional gunk would work its way onto the operative surfaces and the actuator would start hanging again. The switch transition was exacerbating it, but the real issue was getting ALL the gunk out of those crevices. I was avoiding total disassembly of the score reel, but as a result I had to clean it about 15 times.