sick disk

[walls%ssl.span@FEDEX.MSFC.NASA.GOV]

Greetings!  I wonder if someone could help me.  My 3620 has gone belly
up, and has been that way for a while.  At power on, the FEP prompt comes
up fine, and the disk makes its normal(?) awful noises.  When I try to do
a HELLO, though, the machine comes back with a "Drive not ready during unit
select" and goes no further.  This is on a 3620 with two Maxor XT-2190
190 MB drives and a tape drive.

Call maintenance, right?  Well, due to an administrative error, our maint-
enance contract has lapsed.  I described the problem to Symbolics, and the
prognosis was a probable bad control board.  They quoted $3000 plus the 
service call to come fix it.  Here's the deal-- our local maintenance people
have the same disk drive on hand (same rev and everything) and can get what-
ever is wrong with the drive fixed for under $1500 (or replace it, for that
matter).  Do I have everything I need but the knowhow to format the new
disk and bring the machine back up from tape, or a networked machine?  Would
I be risking destroying the new disk drive by putting it in?

Also, what about installing my own second drive in my single drive 3620.
Are such user mods a serious no no?  That machine is still under maintenance.