Would it have been possible to send a manned mission to Mars using Apollo technology? To clarify, I am writing a science fiction story in which a manned Mars mission in 2025 discovers a previous manned mission to Mars sent in the 1990's using modified Apollo lunar technology. Even though it is science fiction I want my story to be as scientifically accurate as possible. For example I have researched methods of shielding from Solar and Cosmic radiation such missions would require and I have surmised that the 21st century mission uses Hydrogenated Boron Nitride Nano Tubes, whilst the earlier mission used a form of polyethylene shielding.
I realise the technology would have to be significantly modified, but would it have been feasible to send a manned mission to Mars using Apollo technology?
I realise it would probably be unfeasible that something like this could have been kept secret,  but it is science fiction, this is hypothetical, that is a plot point I can work out.
 A: 
Does the Saturn V booster rocket use a different propellant than the
  Command/Service module motor? What exactly were the propellants used?

The first stage of the Saturn V launch vehicle burned kerosene and liquid oxygen (LOX) while the second and third stages burned liquid hydrogen and LOX.
The Service module engine burned hypergolic propellants, Aerozine 50 and nitrogen tetroxide.
There is a well researched hard science fiction novel by Stephen Baxter, "Voyage", that is an alternate history in which Apollo type hardware was extended and used for a human landing on Mars.
A: There was a proposal for a Saturn V based flyby mission past Venus. A version of the Skylab was proposed to flyby Venus with astronauts. A similar configuration might have been cobbled together for Mars. However, actually landing on Mars would have been a challenge way outside space technology at the time.
The big problem is radiation. A solar coronal mass ejection (CME) sends $1$KeV protons into space. At $1$KeV $(\gamma~-1) mc^2$ $\simeq~10^{-6}mc^2$, giving the Lorentz gamma factor $\gamma~=~1~+~10^{-6}$. With $\gamma^2~=~1/\sqrt{1~-~v^2/c^2}$ this means $v~\simeq~1.4\times 10^{-3}c$ This is about $420km/s$. There is no chance of out running this or even avoiding it with a Hohmann transfer orbit to either Mars or Venus. A charged particle from the 
CME impacts the material of the craft and emits X-ray by Bremsstralung radiation. This could be lethal, and over a two year mission the crew could be exposed to several of these radiation events.
The lunar module would not have been able to land on Mars. It was designed for the moon with $1/6$th the gravity of Earth and Mars has $.38$ Earth gravity. There is also the problem of atmosphere, so heat shields would be needed. Parachutes and other impliments would probably also be required and this really requires an entirely different landing machine than the Apollo LEM. 
The Venus flyby never reached program design level. The risks and problems were too high. A similar Mars program would have been also risky.
