^Yes. The bolts are TTY (Torque To Yield) which is one-time use. Many has reuse the bolt without real issue, however.
I would never pressure wash the engine anyway since you will force water to places it shouldn't be. The risk is too much. Garden hose is fine but pressure washer is not, IMHO.

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00 E39 DINAN S1 //M5 (82k miles)
06 E53 DINAN 4.8iS, born 2/18/2006 (126k miles) http://www.xoutpost.com/bmw-sav-foru...s-my-dslr.html
90 Straman Z32 TwinTurbo Convertible, (1 of 44 ever made) 5 speed, 444rwhp/451rwtq
01 360 Novitec Spider F1 (26k miles)