The glow plugs usually last me pretty long im not sure how long in terms of tanks but they last me long enough for my taste.

You will definately be happy with teh Fantom engine or the OS engine they are both great engines have both one in an RS4 3 and one in my XXX-NT.

Im not sure what kind of shaft the Original rs4 needs but if its the standard threaded shaft the it should work fine.