I own a 92 SC300 5-speed.
I, too...have experienced what you are describing...except on a much smaller scale.
I notice that when I first warm up the car and proceed to drive out of my driveway, the first time I step on the brakes...the fan will somewhat lose a bit of power for a split second. Then, it will come back on w/ no problems at all.
I haven't been too picky about it, as I don't have the time to diagnose the problem.
I'll try and diagnose it this weekend.
While I was doing an oil change this weekend...(from under the car) I did notice a ground wire that is approximately below the oil filter area. It was caked w/ dirt and grime...so I just cleaned it off. I haven't yet given my car a thorough cleaning (as I'm pretty obsessed w/ stuff like this)...but plan to do so shortly. I don't know if cleaning this wire was beneficial...as I wasn't thinking about it...but thought I would mention as it is directly below the oil filter and prone to getting dirty.
Will give the car a good cleaning soon (hopefully this weekend) and will let you know of the results.
Dom