Hydraulic Fluid

Quick facts :

• Use Castrol RR63 because Mineral oil will attack your seals.
• Castrol RR63 supplies lubricating elements that are required (lacking in DOT3)
• 2,5 liters (4,5 imperial pints) of hydraulic fluid are necessary to fill up the complete hydraulic system.
• Needs to be done every two years because break fluid attacks the circuits even on a resting car
• YAK363 is supposed just as good and less expensive (see below)

Gathering infos on the subject here ...

Good brake fluid has to be incompressible and to resist to high temperatures (prevent boiling and vaporizing inside the circuit), it also has to lubricate the hydraulic pumps.
There are basically two types of hydraulic fluids : DOT fluid or Mineral Oil. DOT is the most commonly used today. Its two major components are from 20 to 40% lubricant and 50 to 80% glycol ether, which determines the fluid's boiling point and viscosity.

As written in RRtechnical#15"The initial recommendation, Castrol Girling Amber Brake Fluid 1738 was used until the late sixties until Castrol came up with the now well known RR363 which was used until the advent of the Silver Spirit in 1980 when the hydraulic systems changed to mineral (LHM) fluids To this day new owners writing on the various web forums will enquire whether RR363 is compatible with DOT3 and DOT4 brake fluids and the advice has always been stick to the RR363 which was developed for the purpose The main worry is keeping the plunger pumps lubricated; if they are not wear can be incredable and pumps are very expensive items to purchase. "

But as Waples puts it : "except for 50,000 series, Camargue and Corniche, the correct brake fluid is Castrol RR363 [..] which is similar to DOT3 type except that it has an additive package that deals with the constant action of the hydraulic pumps."

As RR363 is costly, here is an alternative (found on Topix Forum):Due to the high cost of RR363 hydraulic fluid many Shadow owners are turning to YAK363 instead. This fluid is made by adding 10% or more castor oil to any DOT3 or 4 hydraulic fluid which is pretty much (but not exactly) how RR363 is made. This is far from a new idea and has been around for many years with no complaints about hydraulic damage from its use. However if you go above 20% castor oil (not recommended) there are indications that it can cause 'clumping'/cloudiness in freezing conditions.

Another comment in favour of YAK in RR forum
The reason RR specifies the use of RR363 is it contains a lubricant for the hydraulic pumps.YAK363 is a mixture of 90% dot3 brake fluid and 10% castor oil. There is another variant called OMAR363 which is 85% dot3 and 15% castor oil. The castor oil provides the lubricity. There has been considerable debate on the use of YAK/OMAR363. Some owners won't touch it and others have used it for years with no problems. It is up to you to decide whether they want to "risk" using these RR363 alternatives. For my part I have now been convinced that YAK363 is ok to use and will be converting to it this summer when I carry out my 2 yearly hydraulic fluid change.
You can read more on the RROC-A forum, using the search facility.

Detect Ageing liquid
According to Marinus Rijkers "The ageing of the fluid can be determined by the smell in the reservoir".