Buicks have low oil pressure that is a design "flaw" from it's inception.
From the V8Buick site
The oil pump is integrated into the aluminum front timing cover, not connected to it, and because the steel pump gears spin inside the soft aluminum housing, and wear it prematurely, we suffer from oil pressure issues.
Darryl Roederer, A.K.A. "Professor Buick"
To cure the oil pressure problem, a booster plate and/or an adjustable regulator can fix the problem if the price of a new timing cover is out of your reach.
The booster plate goes between the the timing cover and the oil filter housing. It is a 1/8" steel plate which prevents wear to the oil filter housing surface. This surface is aluminum and by adding the booster plate it will not wear into this housing as it would without because the steel gears of the oil pump rides on this surface.
Oil pump booster plate kit is designed to increase the oil pump's pressure and efficiency over a stock pump. This is not the same as installing the high volume, high pressure oil pump kit, but our oil pump booster plate will increase oil pressure on all Buick oil pumps.
The adjustable regulator helps you increase pressure of oil by way of putting pressure on the oil pump spring. On the outside of the cover you will see a nut that it is about 3/4" in diameter... inside this is the spring.
Both of these are available from http://www.taperformance.com/
which specializes in Buick engines.
V8 and V6 Buicks timing covers will interchange with this exception, the V-6 has a bolt-on timing mark indicator and the V-8 one was cast in. There is also a fuel-injected T/C for V6's (87 and up) that will work and allow for other mods down the road (supercharging, turbocharging, big NOS shots, fuel injection).
You may have to drill out the guide holes of the T/C to install a late model (82 and up) water pump, (big dimple in center), which was redesigned for even water flow to both heads.
Factory GM V8 number 1258617
Factory GM V6 number 12337249
TA Performance number 1530
AE Clevite Engine Parts 6018091
Pioneer Prods. 500231 TIMING COVER: OE# 25505753