For the precision Daedal gearheads, the recommended replacements are:
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PEN
PEN60 is PV60FN
PEN23 is PV23FE
...
PEN115 is PV115FN
PEN42 is PV42FE
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PER
PER60 is RX60
PER23 is RX23
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PER115 is RX115
PER42 is RX42
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PTN
PTN40 is PV40TN
PTN60 is PV60TN
PTN80 is PV90TN
PTN120 is PV115TN
...