Are the factory engine mounts really liquid filled?

[Cobra Jet]

I've read on a few forums that some folks say the original M42 engine mounts are liquid filled - is this true?  If it is true, what type of liquid is impregnated into the mount?

What is everyone using for replacement engine mounts when the originals are in need of replacement?

[tjts1]

Original mounts are oil filled and about $90 a pop. Some people use solid E28 mounts but they will increase noise and vibration. I only replaced the passenger side mount. It takes almost all off the compressional load from engine torque and its exposed to much higher temps from the exhaust. The driver's side mount is generally in much better shape.