I want to know which are the biker proof deisels to own? I want to buy a 1987 300d turbo. Does that motor have a good motor?

I am guessing you are a Brit, since "motor" means "car" over the pond (at least on Wheeler Dealers). Not sure how "biker proof" translates. The 86+ 300D diesels are 6 cylinder, with an aluminum block. I understand they are less bullet-proof than the earlier 5 cylinder iron block engines. The cars do look more stylish though (matter of opinion). Actually, non-turbos are more reliable. In the U.S., all 82+ 300's were turbo. A 240D 4 cyl diesel (non-turbo) is probably the most reliable, but much lower on HP.

The original head can develop cracks if overheated. The head casting was superseded a number of times. Any of the later heads can far better resist cracking. Electronics control idle and emissions. Emissions systems are easily defeated (for diagnostic and off-road purposes). Electronics issues shouldn't strand you.

Alternatives in the 124 series are the 90-93 300D 2.5 which is similar to the '87 but short a cylinder. No cylinder head problems. Converting the EDS controlled vacuum wastegate for an independent pressure actuator will save you needless hours of emissions diagnostics. And the '95 E300 which has a naturally aspirated 16 valve DOHC variant of the '87 300D engine. You get the refinements MB added to the series over time, access to more factory options, and an engine that loves to rev but not quite snap your neck. Glow plugs can break in the head during replacement turning an afternoon job into pulling the head.

Sixto
87 300D

Aluminum head, iron block.

The OM602 in the 90-93 300D 2.5 is a 5 banger.

Sixto
87 300D

Which also appears in the 87 190 2.5 turbo diesel.