tic-tic-tic Cozy Counterflow w/Robertshaw ignition

I 'googled' and found pieces parts of answers to this problem, but nothing conclusive, so I'll start anew:
We have a Cozy Counterflow wall furnace Model CF558B. Bought and installed in 1996. Originally propane, converted professionally to Nat. Gas. in 1998. Unit has a RobertShaw SP735A ignition control.
Problem: the furnace takes about 15-20 seconds, occasionally up to 45 seconds to ignite when turned on. The pilot lights immediately, but the furnace keeps sparking and sparking (that's the source of the tic-tic-tic). Sensor does stick up well into the pilot flame. When furnace finally does light, it operates normally.
Attempted Fix 1: Had the local furnace company who did the conversion come back and adjust the furnace. After paying over $200 for the service call, the problem returned after a few months.
Attempted fix 2: I bought and installed a replacement sensor, trying the easy fix first. No change.
So, I guess the next option is to replace the RobertShaw SP735A ignition control. From what I've found and read:
- many feel the RobertShaw ignition modules are poor quality and recommend replacing with a Honeywell Universal module.
- there was mention of a recall of RobertShaw equipment, but I could only find information about old 1984 recalls of LP valves and a new recall of scuba equipment.
So my questions:
1) Does this sound like an ignition control problem? Are the Honeywell universal ignition modules really worth the $50+ more than just purchasing a replacement RobertShaw?
2) The parts list for the furnace list different pilot assemblies for Nat. Gas and LP. I don't recall the pilot assembly being changed when the unit was converted to Natural Gas. Are the pilot assemblies so radically different for each gas that this could be causing the problem?
3) The parts list also lists two different ignition modules for each gas. Does anyone know if the RobertShaw SP735A is the Nat. gas or the LP ignition module? (I also have a email into Louisville Tin asking this...)
4) Has anyone heard if there is a recall of RobertShaw ignition controls, specifically the SP735A? Details?
Ron Thomas Estes Park, Colorado

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