Penrite DOT 3 plus Castrol oil alternative to RR363
Read this thread (oct 2015) http://au.rrforums.net/forum/messages/17001/18735.html?1444430939
This is a link to the official document by Penrite
Here online shop where to buy from PENRITE
Source: The Rolls-Royce Forum - Australia

Shadow fluid characteristics
All brake fluid is ideally incompressible for positive feel, non-reactive to preserve the integrity of the seals, and will not vaporize in the presence of the heat generated by the brakes. In addition, brake fluid used in the Silver Shadow needs to lubricate the engine driven hydraulic pumps.
Source: The Shadow's Owner Companion, book by Jon Waples - © 2006 Sherbourne Mews, LLC

Quantity of fluid needed for a flush
Five quarts (4,7 litres) of RR363 are needed to flush the brakes and the hydraulics in their entirety.
Source: The Shadow's Owner Companion, book by Jon Waples - © 2006 Sherbourne Mews, LLC

Necessity to change fluid every two years
Any brake fluid is hygroscopic (tends to absorb moisture from the environment). Moisture laden brake fluid vaporizes at hight temperature and this decreases the brakes performances especially at hight speed. Moisture in the system also corrodes the ferrous elements. It is rust that gives old liquid an iced tea colour.
The neccessity of the liquid renewal is then related with the climate : often if humid, less of arid.
Source: The Shadow's Owner Companion, book by Jon Waples - © 2006 Sherbourne Mews, LLC

Attacks paint, leather ..
RR363 will remove the finish of any painted or laquered surface, including the engine bay, exterior paint, interior wood and leather.
Source: The Shadow's Owner Companion, book by Jon Waples - © 2006 Sherbourne Mews, LLC

Fluids mix
Dot 3 and Dot 4 will happily mix with RR363.
Source: The Rolls-Royce Forum - Australia

Refilling the hydraulic tank
Run engine for at least 3 minutes. Use sight glasses on side of the reservoirs to quickly check level. Refill with absolutely clean (sealed) liquid.
Source: Diverse

Alternative mixtures to RR363
Quick recipes from forum :

Recipe's name	Base	Additive - lubricant	Additive ratio	Cl for 1 liter	Cl Total (for 4,7 liters)
Bob UK's	DOT3 or 4	Castor oil	1/2 pint total	6cl	28cl
OMAR363	DOT3 or 4	Castor oil	15%	15cl	71cl
YAK363	DOT3 or 4	Castor oil	10%	10cl	47cl
Citroenists	DOT3	Castor oil	9,25%	9cl	43cl

Source: The Rolls-Royce Forum - Australia