Steam Engine Design/Oiler
Adjustable, gravity fed oilers hold a reservoir of oil and controls it's release through a valve.
The "ACL Oiler 1 PT 3/4"-16 Mounting Stud Trico 32016" from Summit Pumps, Inc. for $124 is an example. See http://www.trico-oilers.com/ACL-Oiler-1-PT-3-4-16-Mounting-Stud-Trico-32016-32016.htm
Another example, with more data is found at http://www.deanindustrial.com/tr-kgoil.htm (Dean Industrial). See spec sheet at right. Note restrictions on temperature and vibration. The KG Oiler has a max temp of 250 degrees. Atlas Oilers in glass also operate up to 250 degrees.
A wick fed oiler uses a wick to provide slow, controlled flow of oil.
The "Type N Wick Feed Oiler 4 oz 1/4" NPT Trico 30742" from Summit Pumps, Inc. for $25 is an example. See http://www.trico-oilers.com/Type-N-Wick-Feed-Oiler-4-oz-1-4-NPT-Trico-30742-30742.htm
More data at http://www.deanindustrial.com/tr-wefeoi.htm.
It looks like the wick fed oilers provide the most amount of control (drips per minute) for the lowest price. A red/white wick gives a moderate slow speed, about a drop ever two minutes (see specs). However, they have a max operating temp at 165 degrees.
Recommend the "Trico 30742" for $25 for the Steam Engine, if temp can be assured.
Adjustable rates of flow can be gotten with an oil flow valve.
The "ST Valve Dbl Fem 1/4 NPT Right Angle Glass Sight Trico 32404" from Summit Pumps, Inc for $36 is an example. See http://www.trico-oilers.com/ST-Valve-Dbl-Fem-1-4NPT-Right-Angle-Glass-Sight-Trico-32404-32404.htm
Dean Industries at  provides more information on ST Valves.