It could be engine oil (which ranges from golden to black, depending on how "appreciated" it has been).
If actually on or under the tire, possibly hydraulic oil from the oleo. That would be red, though could appear clear compared to engine oil. Look on the chrome part of the oleo strut, is it wet at all?
If the oelo is leaking, a servicing is required which is very common after years in service. The servicer must be compotent, or expensive damage can be done taking it apart. Do not operate the plane with low fluid, a simple but effective metering system depends upon the right amount of oil to properly absorb the shocks.
If not that, could also be the shimmy damper. Again, do not fly, if it has leaked down. Look for wet on it's chrome shaft...