CU-SEAL RING ... standard copper washers like you get at hardware stores, 12mm and 22mm.
"gasket".....ah! must be this:
GASKET FOR OIL FILTER HNBR
...the one for the oil tank screen. Is that the green o-ring?
I thought I'd bought a couple of all of them so I could get the sizes, but I didn't get that one, maybe it was too expensive. Not specified as an ordinary / DIN o-ring. But joe's is ok and he changes his oil a lot.
wrt to that...yes, replacing the copper seals and the o-rings is "cheap insurance" / good practise, but if you change your oil very often like I do, and you pay the KTM price - like 10x the normal price for a copper washer or an o-ring, and you use expensive oil, it is not cheap. And that seal for the tank screen filter..well, no ways does that need changing every few thousand km.
Here are some of the o-rings and copper seals that might be useful, that I just copied.
oil engine drain plug seal : CU-SEAL RING DIN7603 22x27x2
oil tank drain plug seal : CU-SEAL RING DIN7603 12x18x1.5
oil filter cover seal : O-RING 40X2,50 NBR 70
oil level sight tube seals : CU-SEAL RING DIN7603 8X12X1
gear position sensor seal : O-RING 27,5X2,5 NBR
brake line banjo seals : CU-SEAL RING DIN7603 10x16x1
water pump tube seals : O-RING 25X3 NBR 70 (2)
THERMOSWITCH LC8 102DG seal : O-RING 17X1,5 NB75
I'm going to go to an o-ring supplier and get a few of the o-rings. NBR or Viton, as lon g as they're not cheap chinese ones.
The copper washers, I've got all except the 22mm for the engine drain plug - but again, I've changed the oil in my Pulsar about 6 times in about 4000 km and the aluminium drain plug seal doesn't leak.