My IS came with NGK DCPRE spark plugs and have worked very well they cost about $4 each.

Recently ROTAX have decided to say you must use their own which are 10X the price.....

IMHO this is BS....

but what do others say ?

I say, you missed the 8.  

NGK DCPR8E

Othewise, you can buy EIGHT of them for under $25 or ONE of the new style for $30

Section 1.1 of Si-912-027 states that " It is not mandatory to retrofit engines which are currently equipped with old spark plug types ... "

From which I Infer that it is also not prohibited to retrofit the Old Plugs into engines currently equipped with the New plugs.

 However, it sounds like they don't want you to mix the old plugs with the new spark plug connectors.

They don't want you to mix the Old Plug with the New Plug.

Or, Mix the Old Connectors with the New Connectors.

Either Connector can be used on Either Plug, it is just that all the Plugs or Connectors need to be the same.

So, Old Plugs with New Connectors is OK!

The difference in the connectors is that one is 90° and the Other is 45°.

They both will fit properly on either plug.

Thanks for the quick response. 

I checked the plug number in Ngk site and got few plugs with the same letters but with more  letters so I'm not sure which one is the one:

DCPR8E BLYB

DCPR8E IX

DCPR8E KC

DCPR8E KP

DCPR8E SOLID