these are Seben "Commando" goggles
They´re using really cheap low quality glass tubes in gen.1.
I think your problem is, that they generate a really milky picture.
That is not a dirt problem, it is a tube problem.
You will not be getting a better image.
Usually on top of the "middle tube" should be a little switch to turn on the IR-illuminator.
The goggles as itself should produce a thin high level noise, when switched on.
And Stephen L is absolutelly right. Forget to consider a repair. It is not worth the money.