I have a 1983 300d turbo that had its transmission rebuilt around 30k miles ago. The car sat in a barn for 15 years and I had to drive it for around 500 miles before I drained and refilled the transmission/torque converter with oem filter, gasket, and mobil fluid from the local Benz dealer. It has started getting cold here and my original problem was the transmission would need to be warmed up and driven 1-2 miles before it shifted up and down correctly. After the drain, only 4qts came out of both. After the flush I put 4 quarts initially, then 2.5 more quarts in and it drove/shifted great. 4-5 days later the shift from 1/2 or 2/3 was jumpy from every complete stop so I put another quart in as advised from the dealer. The problem was fixed once again. 4-5 more days later the transmission must be warmed up again before it upshifts correctly. In total it has 7.6 quarts which I read is the max capacity of fluid with about 200-300ml of lucas transfix added to try and fix the problem. Even after being driven for 20+ minutes and I run it through all the gears for 5-6 seconds, the dipstick is still not showing any fluid level. Should I put more fluid in and test, or could this be vacuum modulator related even though the problem disappears after more fluid is added

If it's not showing fluid on the stick when idling in neutral after a 20 minute drive, then it's either low, or you've got the wrong stick. Low fluid is more likely.

When mine was an automatic it always wanted to hold first gear a little long for the first half mile or so and then shifted great except for when it was hot out.

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Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 400,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 22,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.

Fluid cannot be checked when the car is idling in Neutral.

The fluid must be checked, when car is at operating temperature after a short drive. Then with the car idling in Park...pull the stick, the fluid should be between the lines.

After the fluid is at the correct level, then can you start looking at other things that may cause this issue.

I had an issue with my transmission, where I couldn't get it to up shift....it turned out that when the transmission was rebuilt, the idiot didn't install the correct nut and stake it as they should have...the nut backed out, the yoke separated and also they didn't replace the rear seal.

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It can be difficult to read the fluid level on the dipstick; especially with fresh fluid. I suggest dipping, wiping, and checking the level on the stick several times to make sure you are getting an accurate reading. You may need to look at the stick at a different angle or lighting situation to see the fluid.

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1991 F250 super-cab 7.3 IDI. (rebuilt by me) Banks Sidewinder turbo, hydroboost brakes, new IP and injectors.
2003 S430 - 107K
1983 300SD - Tanoshii - mostly restored ~400K+.
1983 300SD - Good interior. Engine finally tamed ~250K.
Monark Nozzle Install Video - http://tinyurl.com/ptd2tge

Check for leaks, you may be losing tranny oil.

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85 300CD Signal Red/Tan sold
83 300D Manganese Brown 109K
97 E420 Midnight Blue 197K sold
98 BMW 328i Vert White 100K, sold
95 BMW 525i White 125K, sold
93 BMW 525iT Red 193K, sold
95 E320 Green Wagon 125K, sold
94 E320 White 127K, sold
85 300SD 156K Grey (Annie), sold
84 300D Lapis Blue 170K (Judy), sold
99 ML 320 Black (lease), 1998 C230 White (lease)
00 Honda S2000 Red (lease)
86 Mercedes 300E (sold)
84 Porsche 911 Red (sold), 1965 Porsche 911 White (sold)