This is email I send to somebody. Just put here unedited. You may find it useful.

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Hello John,

I have a few AVOs here, and most have the same problem. One work really smooth, indicating how they can be. From the worst one, I had switch fully apart to clean it, that didn't solve the problem.

It was incredible dirty inside.

At first it was ok, but after two years it got as stiff as before. This is where I stopped investigating it.

I believe the explanation is not dirt or lack of grease.

The material is probably bakelite. This is a baked compound of resin, grinded stone, and some other.

Most plastics over the decades alters it's size and hardness. Old switches detoriate slowly. Though bakelite seems pretty well preserved always, my impression is, it does alter it's dimensions in the switch. That's why they get stuck. I think to cure it, you need to take the switch fully apart, and grind each wheel a little thinner. I never tried it, but I think that's the solution. There is some lubricant in there, originally. I don't know what that was, but it's important to use the right one, because lubricants tend to penetrate plastics, increase the size of the object, and because it penetrates, the lubricants disappears too.

So adding more and more lubricants may makes things worse when the switch is stuck. I think grinding the wheels a tiny fraction thinner, and then apply as little lubricant as needed. Theoretically the wheels itself need no lubricant, as the friction is only on the metal switch part of it, and even that is little surface, and self cleaning.

Since there was lubricant inside anyway, I used vaseline. Though this may as well been lubricant by pre owners... So you can't really say.

Vaseline is known to penetrate some rubber badly. It can swell up to 2x the size. Others don't react at all.

As bakelite is quite a crystallized structure, probably any lubricant will penetrate, and there was lubricant used originally, so I choose for vaseline anway. Reason is, it doesn't react with air over time, as does almost every other lubricant there is. Actually the original lubricant looks to me having reacted with air, that's why a stiff switch does get a litte better from usage, but soon gets stiff again.

Instead of vaseline, I think I found something better now, but I have not tested it.

1950's hammond organs tone wheels, have a huge gear box with hundreds of bakelite tooth wheels in it. They need lubrication, for which you needed special receipe "Hammond oil". Use any other oil, and the wheels get stuck over time. So this oil can lubrucate bakelite. You can buy "so called" original old hammond oil on ebay, but people in the Hammond club don't trust it. Any fake oil, and the wheels get destroyed over time. There is a good new made oil, that is by Pressol. It is oil number 10596. I add a pictures to this email. So this is long time proven to be non-reactive with bakelite, by some people of the Hammond club.

Even so you might try to just oil your switch with this, though I am not confident it will help for a long time. I do know a good switch rolls really easy and light. Next time I lubricate a roller switch, I would use this oil, and grind the wheels thinner when the switch is all apart. That is easy to do. It's just a lot of work.

Hope this is of any help to you.

Good luck with it!

Jac

----Original Message-----
From: pentagrid@xxxxx.nz
Sent: Sonntag, 7. September 2014 08:09
To: jac@xxxxxx.de
Subject: Sorry to Bother You...

I am a proud owner on an AVO MK4 tester which works very well apart from one frustrating feature.

The selector switches in the roller are extremely tight. On average, after two settings have been used, my fingers are very tired & hurting - that's how tight they are.

Can they be lubricated please? & if so, with what? I have resisted the urge to spray WD40 between the selectors.

Kind regards,
John Roberts