Yes hydraulic fluids that are compatible with 5606 are 83282 or 87257. They are synthetic and fire resistant. There is a thread in here talking about the new fluids and whether they are approved in our Mooneys by Mooney.
Hydraulic Fluids
Most aircraft manufactures require specific fluids for their hydraulic systems. Always refer to your aircraft manufacturer's maintenance instructions for the proper fluid.
All Grove brake systems incorporate Buna-N (Nitrile) O-Ring seals that are compatible with MIL-H-5606 hydraulic fluid which has been the aircraft industry standard for many years.
MIL-H-5606 hydraulic is a mineral-oil based fluid with excellent operating properties over a temperature range of -65°F to 274°F. A major deficiency of MIL-H-5606 is its high degree of flammability. Because of this, the commercial aircraft industry has developed and uses hydraulic systems based on phosphate-ester based hydraulic fluids. However, these fluids ARE NOT compatible with MIL-H-5606 or its systems.
The military led the way in developing a more flame resistant hydraulic fluid that is compatible and miscible with MIL-H-5606. As a result, a synthetic-hydrocarbon based fluid MIL-H-83282 (now MIL-PRF-83282) was developed which is superior to MIL-H-5606 (now MIL-PRF-5606) in fire resistant properties, but lacks good qualities in low temperature viscosity.
More recently MIL-PRF 87257 was introduced in order to address the concerns over the low temperature viscosity weakness of MIL-PRF-83282.
Bottom Line: MIL-H-5606 has been replaced with MIL-PRF-83282 and MIL-PRF-87257. Each of these fluids, and their associated systems, are compatible and miscible with each other. You can mix any combination and/or amount of these fluids together without any ill effects.
If, and/or when, you change over from MIL-H-5606 you can either:
1. drain your hydraulic system and refill with MIL-PRF-83282 or MIL-PRF-87257, or
2. merely top off the reservoir with MIL-PRF-83282 or MIL-PRF-87257 as needed.
Both methods have been used with great success with no reported problems