How do you tell if you have an as41 case ?
and if it isn't is that such a bad thing.

It says so!

under the tubes on one side of the motor it is cast in.

It could/should be either a AS41 or maybe a AS 21

The as 41's are the "standard" mag case. Dual relief etc etc

The AS 21's are a bit rarer and have a higher aluminium content.

Then there are the new aluminium cases. Dont know anyone who has run them

yeah the new cases are heavier... n much rougher on the insides from being sand cast in lieu on die cast like the magnesium cases.

there suspost to be stronger ect etc time will tell