straight6pwr said:

From the e34 bentley, which specifies one torque spec for the range of manual transmissions, even though ZF and Getrag were used. I highlighted the specs in red below. 

Output shaft oil seal, replacing
(transmission installed)

1. Remove complete exhaust system. See 180 Exhaust
System.

2. Disconnect driveshaft from transmission. See 260
Driveshaft.

3. Remove output shaft flange.
• Bend back and remove nut lockplate. See Fig. 2.
• Hold flange steady and remove the collar nut (use 30
mm thin-walled . deep socket).
• Remove flange. If necessary. use a puller.

4. Using a seal remover or screwdriver. pry out old seal.
Lubricate new seal with oil and drive into place.

CAUTION DO not damage the transmission case housing
when prying out the old seal.A damagedcase can
result in oil leaks.

5. Reinstall flange to output shaft (and shims. if applicable).
Coat bearing surface of collar nut with sealer and
install nul.

NOTE -
• BMW recommends the use of a sealer such as Loctite
242 when installing the collar nut to prevent oil
from leaking past the threaded shaft.

• On Getrag S5D 250 G transmission. BMW recommends
heating the output flange to about 176'F to aid in installation.

6. Tighten collar nut in two stages. Install new lockplate.
Bend tabs into flange grooves.
lightening Torques

• Output flange to output shaft
stage I 190 Nm (140 ft-Ib)
stage II (after loosening) 120 Nm (89 fl-Ib)

The two stage tightening is what I have read before as well, so I think this is what I will need to do.

jc43089 said:

If you over tighten it I found out that the transmission case will explode and lock up eventually.  Typically this will happen when your wife is driving with her mom to get their hair done before your sister-in-law's wedding.

It always happens at the most convenient times.

Output shaft oil seal, replacing
(transmission installed)

1. Remove complete exhaust system. See 180 Exhaust
System.

2. Disconnect driveshaft from transmission. See 260
Driveshaft.

3. Remove output shaft flange.
• Bend back and remove nut lockplate. See Fig. 2.
• Hold flange steady and remove the collar nut (use 30
mm thin-walled . deep socket).
• Remove flange. If necessary. use a puller.

4. Using a seal remover or screwdriver. pry out old seal.
Lubricate new seal with oil and drive into place.

CAUTION DO not damage the transmission case housing
when prying out the old seal.A damagedcase can
result in oil leaks.

5. Reinstall flange to output shaft (and shims. if applicable).
Coat bearing surface of collar nut with sealer and
install nul.

NOTE -
• BMW recommends the use of a sealer such as Loctite
242 when installing the collar nut to prevent oil
from leaking past the threaded shaft.

• On Getrag S5D 250 G transmission. BMW recommends
heating the output flange to about 176'F to aid in installation.

6. Tighten collar nut in two stages. Install new lockplate.
Bend tabs into flange grooves.
lightening Torques

• Output flange to output shaft
stage I 190 Nm (140 ft-Ib)
stage II (after loosening) 120 Nm (89 fl-Ib)