I visited our local bearing shop at Mansikkala area and they also recommended using X-rings. It seems that the original sealing is kind of square box shape which has a groove on axle facing side that is filled with some sort of foamy stuff. So X-shaped sealing is the closest one generally available product.
Unfortunately they did not had correct size X-ring available and it would have been an order from somewhere longer distance (inside Europe though). They had normal O-ring at that size, but I did not want to take that.
I drove to my favorite hydraulics shop at Kurkvuori area since I knew they also can deliver wide variety of seals and they use a different supplier to order than the bearing shop. It turned out that they were able to order from their supplier X-rings at size I was searching for. The exact size is 5,33 x 46,99mm and I agreed that they will take those when they do their next order to their supplier so I will save shipment costs. So probably X-rings arrive at the end of next week, but I’m not able to fetch them until the week after that due some coming travels. Hopefully the ordered seals will fit to my need, but that we shall see later.
Before the seals arrive I can dismantle the gearbox I taken out from my Sierra at the beginning of 2013 when I replaced also the engine. That gearbox is perfectly OK other vice, but it has also viscous coupling unit surrendered. So I will put this refurbished unit inside that gearbox and I have another faulty spare viscous coupling unit to refurbish sometime later when I have tested does this work as expected or not. 🙂