Opel COMBO Owner's Manual page 162

160 Service and maintenance
temperatures the factory filled coolant
provides frost protection down to
approx. -37°C. This concentration
should be maintained all year round.
The use of additional coolant
additives that intend to give additional
corrosion protection or seal against
minor leaks can cause function
problems. Liability for consequences
resulting from the use of additional
coolant additives will be rejected.
Brake and clutch fluid
Only use high-performance DOT 4+
brake fluid approved for the vehicle.
Consult a workshop.
Over time, brake fluid absorbs
moisture which will reduce braking
effectiveness. The brake fluid should
therefore be replaced at the specified
interval.
Brake fluid should be stored in a
sealed container to avoid water
absorption.
Ensure brake fluid does not become
contaminated.