On January 22, 2009, David Lake in Queensland, Australia, wrote:
"What volume of oil does each shock hold when correctly filled from empty?"

I just spent 20 minutes fiddling with one to get the answer. I had an MGA front shock on my desk for a long time for measurements and drawings, sparkly clean, valve removed, inverted, and pumped completely void of oil. Starting with an empty trigger pump oil can and exactly 8 ounces of oil in a measuring cup, I put oil in the trigger can and proceeded to filled the shock, pumping on the lever to expel any air. When finished I emptied the oil can back into the measuring cup and had 3 ounces of oil left. So the answer is 5-fluid-ounces (150-ml) of oil to fill the front shock.

An additional bit of information is that it takes very close to 4-ounces of oil to fill it enough to get the air out and have good damping action over the full stroke with no gurgling inside. If it leaks it will begin to lose damping action with just a little more than 1-ounce down, and most of the damping is gone by 2-ounces down. So if your shocks are low enough on oil to not work, but they are not completely empty, it may only require a couple of ounces for topping off. I suppose the rear shock is nearly the same volume, as the piston chambers are close to the same size.

Front shocks are horizontal with the top piston chamber above the shaft, so if a shaft seal leaks it may quickly drop the oil level enough to kill the damping action. In years past I had problems with front shocks leaking and problems getting good rebuilt units (Apple Hydraulics haunting me). I finally installed a pair of NOS units about 10-years ago, and have no problems for the past 100,000 miles.

The rear shocks have the piston chambers vertical at bottom with the shaft at top, so they are less prone to losing large amounts of fluid and probably more tolerant of low fluid level. I check and top off front shocks at least once a year with spring, preventative maintenance work. I don't suppose I check the rear ones more than once in five years or 50,000 miles, but I haven't had any reason to think they don't work always, and they are now 50 years old original issue with 370,000 miles accrued.