Transmission fluid question

[LuvNH]

Posted originally in the reverse light switch forum last Thursday night.

Long story short. Have had the car for less than a year. 79 911SC rev lights weren’t working. Upon inspection I found there was no pin in the transmission. Replaced it and lights work, great!

Question- in the process, I lost about 1/8-1/4 qt of fluid. When I checked the level at the fill point on the side, fluid was slowly streaming out. I was under the impression that this alone is an indicator of a full fluid level, no?

FWIW, I noticed during my light switch checks that it seems to shift better now than before losing the fluid. I have NOT driven it yet since.

1. Was mine overfilled previously?

2. I meant to get Swepco 80w90, but got 90w instead. No go?

3. Tranny number (per pic) is 915.61 s/n is 719 1670 what is the /12/?

Many thanks.

[Schulisco]

Use an all mineral transmission oil with SAE90 GL5 specification for normal 915 gearboxes. This oil was originally used and recommended by Porsche. If the gearbox hasn't been overhauled yet the synchros benefit greatly by that oil supporting synchronization due the drag torque.
The "12" in the gearbox number indicates a 40% limited slip differetial from factory! In this case check the oil recommendations from Porsche factory. The oil must be capable to used with LSD.