1985 W123 300TD Transmission leak help
 

Before I take the car into the mechanic I wanted to check with you guys to see what your thoughts are on my problem. I have a 1985 W123 300TD that spontaneously decided to leak out all of its transmission fluid in a couple of days while I left it sitting in the back yard. Leak seems to be coming from between the engine and the transmission... Any ideas on what it might be and what do you think the mechanic will charge? I'll see if Hauer's German Auto Repair can take the wagon next week.

Sounds like the front seal on the trans.

The transmission has to be taken off. It can leak from the front seal (most likely) or from the oil pump gasket (less likely). A failure of the gasket results in a slow leak, so a faulty front seal is more likely.

Only replacing the front seal is not very difficult. Replacing the gasket of the oil pump is time-consuming, as the old seal has to be scraped off very carefully, so that no old gasket parts fall into the transmission.

The bearing of the oil pump (just behind the seal) has to be good too. It can be replaced, but the pump has to come out. You can also replace the seals in the entire pump, but it is not necessary.

The mechanic will charge labour costs for removing and installing the transmission.

I recall that the rubber that holds the lines can degrade. Once that happens, there is metal on metal contact and the tubes get pierced??
Not sure if this is your issue, but thought I'd add this.

+1 on the cooler line fatigue. Check the mounts for the lines and see if you have a work spot.

It turned out to be the transmission oil cooler lines. I purchased 2 lines and it was amazingly simple to change them out. After that I went ahead and changed out the transmission oil with full synthetic ATF from wallyworld. I also including the stuff in the torque converter and put it a new filter and pan gasket. I want to thank everyone for all of their great help!