The XK-E series and 1969 - 1987 Jaguar XJ6 (Engine: 4.2) Ball Joint Boot will fit your lower joint.
I have not found any alternative for the upper joint boot.
Here is further data you need.
W126EngineTrough Danger Zone on the W126
http://www.peachparts.com/Wikka/W126EngineTrough
Suspension Guide Rod Replacement
on the 1985 300SD
http://www.peachparts.com/Wikka/W126GuideRod
Replacing the Rear Shocks & Springs
on the W126 1985 300SD
http://www.peachparts.com/Wikka/W126RearShocksSprings
Steering Coupling Replacement
on the 1984 300D (W123 Chassis)
http://www.peachparts.com/Wikka/W123SteeringCoupling
Vehicle: 1985 Mercedes Benz 300SD
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MB# 126 330 05 03
Fastlane: Tie Rod Assembly, Left
http://catalog.peachparts.com/item.wws?sku=W0133-1619992
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MB# 126 330 06 03
Fastlane: Tie Rod assembly, Right
http://catalog.peachparts.com/item.wws?sku=W0133-1620796
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MB# 126 460 08 05
Fastlane: Drag Link, (Center Tie Rod)
http://catalog.peachparts.com/item.wws?sku=W0133-1619213
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MB# 000 463 51 32
Fastlane: Steering Damper
http://catalog.peachparts.com/item.wws?sku=W0133-1628326
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MB# 126 460 08 19
Fastlane: Idler Arm Repair Kit
http://catalog.peachparts.com/item.wws?sku=W0133-1629430
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MB# 123 460 02 10
Fastlane: Steering Coupling
http://catalog.peachparts.com/item.wws?sku=W0133-1610812
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MB# 116 333 09 27
Fastlane: Ball Joint, Lower - Outer (2 Per Car)
http://catalog.peachparts.com/item.wws?sku=W0133-1628145
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MB# 126 330 06 07
Fastlane: Control Arm, Left - Upper
http://catalog.peachparts.com/item.wws?sku=W0133-1610408
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MB# 126 330 07 07
Fastlane: Control Arm, Right - Upper
http://catalog.peachparts.com/item.wws?sku=W0133-1610107
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MB# 126 333 38 14
Fastlane: Control Arm Bushing, Front Upper Inner (4 Per Car)
http://catalog.peachparts.com/item.wws?sku=W0133-1628670
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MB# 116 333 40 14
Fastlane: Control Arm Bushing, Front Upper Outer (4 Per Car)
http://catalog.peachparts.com/item.wws?sku=W0133-1642615
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MB# 126 330 18 07
Fastlane: Control Arm, Left - Lower
http://catalog.peachparts.com/item.wws?sku=W0133-1598723
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MB# 126 330 19 07
Fastlane: Control Arm, Right - Lower
http://catalog.peachparts.com/item.wws?sku=W0133-1598657
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MB# 126 330 12 43
Fastlane: Suspension Brng Brkt, Left
http://catalog.peachparts.com/item.wws?sku=W0133-1597408
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MB# 126 330 13 43
Fastlane: Suspension Brng Brkt, Right
http://catalog.peachparts.com/item.wws?sku=W0133-1597432
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MB# 126 333 54 14
Fastlane: Bushing, Brng Brkt, Front, (2 Per Car)
http://catalog.peachparts.com/item.wws?sku=W0133-1629427
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MB# 126 333 33 14
Fastlane: Bushing, Brng Brkt, Rear, (2 Per Car)
http://catalog.peachparts.com/item.wws?sku=W0133-1629760
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MB# 126 330 11 35
Fastlane: Guide Rod Mount Kit, Control Arm Stabilizer (Support Joint) Front (2 Per Car)
http://catalog.peachparts.com/item.wws?sku=W0133-1616456
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MB# 123 320 09 89
Fastlane: Sway Bar Link, Rear torsion bar To trailing arm. (2 Per Car)
http://catalog.peachparts.com/item.wws?sku=W0133-1637060
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MB# 126 352 01 65
Fastlane: Trailing Arm Bushing, Control Arm To Subframe, (4 per car)
http://catalog.peachparts.com/item.wws?sku=W0133-1637555
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MB# 126 350 01 75
Fastlane: Subframe Bushing Kit, Front Position of Rear Subframe
http://catalog.peachparts.com/item.wws?sku=W0133-1611451
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MB# 123 330 14 75
Fastlane: Control Arm Bushing Kit, Front Lower Outer (2 Per Car)
http://catalog.peachparts.com/item.wws?sku=W0133-1631144
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MB# 126 330 00 75
Fastlane: Control Arm Bushing Kit, Front Lower inner (2 Per Car)
http://catalog.peachparts.com/item.wws?sku=W0133-1624590
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MB# 123 351 11 42
Fastlane: Differential Mount, Rear Subframe to frame floor.
http://catalog.peachparts.com/item.wws?sku=W0133-1622068
Have a great day.