What type and weight of oil do you use in your gearbox and rear axle?
It seem everyone has a different recommendation. Here is what I've heard
a EP GL5 oil is fine.
use 140 wt rear
use 90 wt rear
90 wt gearbox
Must use a GL-1.
Use of modern GL-5 is OK
Don't ues Gl-5 as it has additives that will destroy soft metals.
Use GL-4 made for classic cars.
Use a hypoid oil as it has lubricating additives
Use a synthetic
There are so many choices one doesn't know which is OK to use.

90 is ok , better EP 90 . Is good for all .

Then there is no worry about the additives in the EP oils damaging the soft metals?

This is a joke ! What kind of soft metal can get damage from what ? And where is some soft metal ? What is a soft metal - babbitt ? How can you belive this nonsens .

Dunno of this is a joke. What I heard is that bronze parts in the dif can be affected by modern doped lubricants. Sulphur is the cause I believe . I was warned not to use modern oil in the dif of my 1960 Healey.

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"Barttore has left the forum"

Sorry , this is nonsense . The last 30 years I build up 6 cylinder Healeys for racing , and all got the same oil .

This is where is says that some oils are not / some oils are suitable for bronze and brass components in gearbozes and difs:
http://www.millersoils.co.uk/automotive/classic-gearbox-oil.asp

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"Barttore has left the forum"

I like it ,
" Classic car engine and gearbox oil "

What is the difference in materials from old engines to new ( later ) engines ?
Name me a material what is in new engines and does not exist in old engines ?
Name me a material what is in old engines and does not exist in new engines ?
Modern oil is much better compared to pre war oil . Why do I need to buy " Classic oil " for an old engine , if a modern oil is better ? What is different in an old engine compared to a modern engine . All parts have less stress in an old engine compare to a modern engine .
It is only Marketing .

Could be - it does not sound logical to me too.

a short search on the "why" found this:
http://www.machinerylubrication.com/Read/28958/ep-additives-effects

Wikipedia also has info:
http://en.wikipedia.org/wiki/Extreme_pressure_additive

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"Barttore has left the forum"

So, are there ANY soft or yellow metals (bronze, brass, copper) in either the gearbox or rear axle of a Bugatti?

There is a lot of nonsense in the internet . One example is , Bugatti Type 5 Wikipedia - just nonsense .
No bronze in the gearbox .

Good evening.
Whilst I bow to all the experts, my Brescia gearbox has a bronze sleeve for the output shaft bearings and bronze housings for the gear change rods.
I used straight 50 oil with no problems over many years. Virtually the same box is in the GP cars (transmitting about 4 times the horsepower when running on methanol) and we used Castrol GP50, but had to change some gearwheels after two or three seasons' VSCC racing.
Trust this is of interest.
Cheers.

The manufactures don't even agree on this. One tech rep told me that he thought that a GL 1 oil (no additives) should be used even though they offer a GL 4 oil which claims to be safe on the soft or yellow metals (there is bronze in both the rear axle and gearbox).
Go figure.