there was no oil-in-frame model. Only the 5 works racers of the second generation were such. Their frames only appear the same; actually they are very different.
This modification has been done by several over here, but none of them (in Germany) are running on the road legally, so not much can be said about everyday usage.
My hands-on experience with one such bike are such, that I cannot warn off enuf. True, that had more to do with the way it was done than with the idea as such. I recently talked about this in this forum. Re the MZ bikes: racing usage is not comparable. Oil is controlled and changed very frequently, engines are broken (both ways) frequently; running time amounts only to a couple of hours between routine checks and changes.
Off hand, I cannot think of anything easily fit, that is worth using. And I have put more than just a
bit of thought into this topic, finally making my own tank.
This, not because of the seat frame which I have retained in much altered form, but because the OEM tank is a piece of crap. The Yamaha SZR tank can be made to fit relatively easily, i.e. the tank and its hoses fit 1:1 but not with the Skorpion exhaust as it is. As OEM tanks go, the SZR tank is good, too; large enuf and with the requisite 1/3 air cavity and higher than wide. Mounted lower than the motor, it does not drain while not in use. It is not round but you can't have everything.
You see the tank which does not ground regardless of leanover. You can also see, that the SZR does not have the downtube of the Skorpion and while that tube does not interfere with the SZR tank at all,it obviously does with the SZR exhaust which otherwise could be used. Shown is the no longer available Termignoni racing system for the SZR with is very good indeed but does not fit the Skorpion because of the black tube.
A XT or Baghira system should fit howerever; I have a XT/TT system on my Skorpion
While this does not fit the 5-valve head, there are very similar header systems available that do and the routing behind the frame is the same. This particular set up from Devil fits as if made for the bike; no changes were necessary. For the water-cooled engine, the radiator would have to be moved forward to clear the headers, something that is necessary for other good racing systems like the Remus Cup system for the Skorpion as well.
The SRX tank is no good at all; too small, too hot.