Similar thing happened to mine. You may find the same thing that I did, in that the two primary gears are press fit together and time, wear, and jams had worn the mating surfaces down to the point where they could no longer hold against the force needed to move the MPF.

Fortunately, (in mine at least) these were brass gears so to deal with the problem I separated them, degreased and cleaned them thoroughly, and brazed them back together. Coming up on five years now and no issues with the motor since!

Would also be interesting in testing/purchasing when this comes together. The MPF in my Doctor Who is getting by but is starting to show it's age/wear...

Still very much interested if/when the opportunity arises. And the timing could be good as I keep thinking toward taking my Doctor Who to MGC in April where it would get some extensive (some might say 'severe') play testing! That would land in your six month window, eh?

OK, guess it is time to step out of the darkness (or Dungeon if you prefer) and state for the record that I am the one who received the B3 kit. Has taken a fair bit longer to get it fully installed and such than I would have preferred, assorted local/personal issues delayed things.

But I think that I am at the point (about 100 games in) where I can offer some observations.

The installation of the kit is actually fairly straight forward, but not for the faint of heart as it does require a bit of drilling, cutting, and some fairly precise measurements for the required modifications to the existing lift frame. Also; I would strongly recommend trying to correct any 'issues' with the lift frame prior to starting to install the kit (frame twisted, mounting ears bent, etc.) since dealing with them after the kit is installed can throw the frame out of square and cause a tilt or binding in the mini-playfield as it moves.

But once installed, the difference is quite dramatic. The mini-playfield is much more 'solid' in each of it's operating positions and much smoother in it's movements. You may find a couple of unexpected things resulting from the added rigidity tho...

* The cushion pad on the 'lock' target should be checked or 'airballs' can become much more common!
* You may find that the shots to the lock saucers seem tighter since the balls will retain more energy.
* Leveling of the front edge of the mini-playfield with the main playfield (especially with 'Cliffy's' installed) is critical, again to keep the number of 'airballs' down.

Also, as I saw a comment in another Doctor Who thread regarding binding after Cliffy's had been installed I would like to point out that this kit has provisions for adjustments on the mini-playfield centering designed in so compensating for the addition of the Cliffy's was about as easy as it gets.

A couple of images of the upgraded unit in it's various positions of play follow. And yes, I know I have a tad bit of leveling to do yet.
There is also a link to a recent video of the playfield in motion. Solid and smooth!

My sincere thanks to Darkpinball for allowing me to be a part of this! I can only imagine what the Mark II version of the upgrade kit will be like!

https://drive.google.com/open?id=17rATPgCvT7xnYVneQns58kdW4DvRpr9u

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